Method and apparatus for detecting movement of a shipping container latch

ABSTRACT

A system, method, and apparatus for monitoring and detecting movement of components of a shipping container latch. A latch monitor may embody an electromagnetic sensing unit and a nearby magnet or light emitter for measuring and characterizing the profile of a nearby electromagnetic field. The field profile is monitored to detect a change in the profile, log the change, and report any abnormal disturbance to the electromagnetic field, indicating a breach of the integrity of a latching mechanism on a shipping container. An alert of a breach event may be sent via a communication network to an authority for response. The invention can distinguish authorized, incidental, and tampering events, and also store and upload an electronic manifest for a shipping container.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

The present U.S. application claims priority from earlier filedProvisional Application Ser. No. 60/981,130, filed Oct. 19, 2007,entitled “APPARATUS, SYSTEM AND METHOD FOR DETECTING ENTRY TO A SHIPPINGCONTAINER,” by Rodney C. Montrose, Mark A. Diener, and John R. Keller.

The present U.S. patent application is related to U.S. patentapplication entitled “LATCH MONITORING APPARATUS FOR A SHIPPINGCONTAINER DOOR;” U.S. patent application entitled “APPARATUS FORDETECTING TAMPERING OF A LATCH MECHANISM;” and U.S. patent applicationentitled “METHOD FOR MAINTAINING A SHIPPING CONTAINER MANIFEST.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to devices for monitoring anddetecting entry to a shipping container. The invention more particularlyrelates to devices and methods that sense, analyze, and interpretmovement of a nearby object to detecting motion of a movable portion ofthe latch mechanism of a shipping container.

2. Description of the Prior Art

In the shipment of goods throughout the world, the use of standardizedcontainers to house the goods during shipment and storage has becomewidespread. Standardized containers provide ease of handling andadequate security of large volumes of goods as they pass through theintermodal transport networks and systems, and international ports allover the globe. A variety of systems, methods, and devices have beendeveloped for tracking and monitoring the containers en route and instorage, as well as managing the routing and handling of containersduring loading, unloading, inspection, shipment, storage, delivery, etc.Other systems, methods, and devices are in use for ensuring security ofthe containers and their contents. These include various kinds of locks,sealing mechanisms, signaling devices, alarms, monitoring units, etc.,designed to detect tampering with a shipping container or its door andprovide an indication of a tampering event therewith.

Standardized shipping containers are rectangular boxes constructed to bejoined with a standardized truck chassis, or placed or stacked on arailcar chassis or shipboard space for shipping from one place (origin)to another (destination). The containers may be manipulated and stackedin a shipping yard for storage, or handling according to routing datafor dispatch to a destination. The containers are typically equippedwith standardized doors at one end. Typically there are two doors,hinged along the outside vertical edge of the door opening, each doorextending the full height of the door opening of the container, and eachextending laterally for half the width of the container. The doors eachemploy a standardized latch mechanism having at least one vertical rodor pole that, when rotated through an angle by a hand lever attached tothe rod, moves a latching arm fixed to each end of the rod into alatched position with a receptacle on the container at the edge of thedoor opening just above and below the door opening. Most such shippingcontainers have two such latching mechanisms on each door. Thus, foursuch rotating rod latching mechanisms may be spaced at approximatelyuniform intervals across the width of the container.

As described herein below, a number of solutions have been disclosed toprovide some sort of sealing device attached to the door or to its latchthat must be broken or damaged to gain access to the container. Somesealing devices provide an indication that the device was subject totampering at some time previous to a first notice of the condition ofthe device. Other devices, such as a switch or other sensing mechanismplaced in a bridging relationship with the door and the container, mayprovide a signal or alarm from the switch or sensing mechanism when thedoor of the container is moved away from the container opening.

U.S. Pat. No. 4,750,197 issued to Denekamp et al. discloses a securitysystem for containers that includes door sensors having magnets embeddedinside each door and Hall Effect sensors positioned on the container tosense the magnetic field of the magnets when the doors are closed.Signals from the sensors may be coupled to a monitoring unit, along withoutputs of other sensors in the container that are responsive to certainconditions.

U.S. Pat. No. 4,841,283 issued to Bubliewicz discloses a two-part hingehaving a rotation detector embedded in a knuckle portion of the hinge,one part a stationary portion having a spaced-apart emitter anddetector, the other a rotating shield plate that rotates into or out ofthe space between the emitter and detector as the hinge leaves are swungabout the hinge pivot.

U.S. Pat. No. 6,069,563 issued to Kadner et al. discloses an electronicseal having a conductive loop that forms part of a circuit for detectingresistance changes in the loop as an indication of tampering with theloop. The loop may be enclosed in a pin or otherwise coupled into a sealbody containing detection and signaling circuitry. A detection event maybe stored or transmitted, and the circuitry may operate in sleep andactive modes.

U.S. Pat. No. 6,265,973 issued to Brammall et al. discloses anelectronic seal configured as a conductive bolt and a cavity havingelectrical contacts in a locking body for receiving the bolt. Thelocking body attaches to a container door. The bolt secures hasps of thecontainer door latch to the locking body, and completes a circuit withinthe locking body. If the bolt is severed or removed, the circuitresponds by transmitting a signal to a local reader.

U.S. Pat. No. 6,281,793 issued to Haimovich et al. discloses anelectronic seal body for receiving both ends of a seal wire andconnecting them to a circuit that senses a change in an electronicparameter, such as a resistance change as described in U.S. Pat. No.6,002,343, that is unreadable except upon disengagement of the seal wirefrom the seal body. The seal body is attached to the object beingprotected. The seal wire may be passed through a movable part of theobject being protected.

U.S. Pat. No. 6,400,266 issued to Brown, Jr. discloses a trailer havinga door, a locking mechanism for securing the door, and a sensor forsensing a closed and secured door. The sensor, mounted on a stationarypart of the trailer, may be a proximity, mechanical, Hall Effect, photoeye, or laser sensor. The sensor may detect the presence or the absenceof a ferrous or opaque object in the locking mechanism. Sensor outputsignals may be used for various control functions.

U.S. Pat. No. 6,747,558 issued to Thorne et al. discloses a seal tag fora container including a locking device, which includes a bolt thatpasses through holes in the arms of a U-shaped member. The bolt alsopasses through the center of first and second coils disposed around theholes in the ends of the arms and the closed ends of a hasp assemblyattached to the container and positioned between the arms. Tamperingwith the bolt affects the magnetic field respectively established andmonitored by the coils, enabling detection of the tampering. Thedetection signal may be transmitted or accessed externally.

U.S. Pat. No. 6,870,478 issued to Cockburn et al. discloses a monitoringunit for attachment to a secured item such as a container locking rod. Aswitch in a mounting bracket of the monitoring unit arms its alarmcircuit when attached and causes an alarm if the mounting bracket isremoved.

U.S. Pat. No. 7,242,296 issued to Wang et al. discloses a door closuremonitor installed on the inside of one door of a container and a doordisplacement transducer mounted in juxtaposition on the opposite door ofthe container. The displacement transducer may be a proximity switch, apressure transducer, or a position switch. The transducer enters onestate or the opposite state depending on the spatial relationship of thetransducer and the closure monitor. An electronic circuit communicatesthe state of the monitor via an antenna.

U.S. Patent Application Publication No. 2006/0103524 filed by Auerbachet al. discloses an electronic seal for a shipping container locksimilar to the seal of the Kadner patent (U.S. Pat. No. 6,069,563). Anelectronic seal wire enclosed in a frangible hollow shaft is configuredfor press-fit engagement with a socket. Breaking the shaft or removingthe pin from the socket breaks the seal. One reusable embodimentincludes a reed switch in the shaft operated by a magnet in the socketportion.

U.S. Patent Application Publication No. 2007/0285240 filed by Carroll etal. discloses a high-resistance cable coupled to a microprocessor thatdetects resistance changes as an electronic seal and stores the time ofthe change in memory. An active RFID transceiver communicates the statuson demand of a remote reader.

U.S. Patent Application Publication No. 2007/0285240 filed by Senseniget al. discloses preferred use of passive RFID devices on shippingcontainers for monitoring by active devices on the vehicle carrying thecontainer or other locations close to the container's position. Theactive devices include GPS and processing apparatus for monitoring andtracking ID and location data.

A common characteristic of the foregoing devices and methods is thatthey employ a digital or binary approach by determining which of twostates exists. For example, whether a door is open or closed, or a sealis broken or intact. Thus, in such systems, tampering is detected as aneither/or event, without the ability to reject false indications thatmay appear to be tampering but actually are not tampering. A furtherdifficulty with the either/or approach is that a “positive” indicationby the prior art devices is no more informative or reliable than alikelihood of tampering. Similarly, in some of the devices, an attemptedtampering event may not be detected or may be in process but goesundetected until a gross change has occurred in the sensing apparatusbeing monitored. Other devices and methods store the detectioninformation for retrieval some time after the detection event actuallyoccurred. Such indications are weaknesses in the security of shippingcontainers and their contents, particularly in an environment where lossprevention and terrorism interdiction are important objectives.

What is needed is an intelligent system, method, and apparatus that candetect, analyze, and distinguish a variety of potential container breachevents, and make the detection information available in real time, sothat accurate and timely information about attempted or realized breachof a container can be developed and made available to shippingauthorities.

SUMMARY OF THE INVENTION

Accordingly, a novel system, method, and apparatus for monitoring anddetecting movement of a shipping container latch are disclosed.Generally, the novel system comprises (A) a magnet attached to theshipping container latch; (B) a sensing unit disposed proximate themagnet for detecting, processing, and analyzing signals from a uniform,predetermined array of a plurality of magnetic sensors for generating adata message containing information describing a magnetic field profileproduced by the magnet in the vicinity of the sensing unit; and (C) acommunication network covering a predetermined area within a geographicshipping infrastructure for receiving signals transmitted by the sensingunit and outputting the data message to a control authority for thegeographic shipping infrastructure.

Further, a novel method comprises the steps of (1) attaching a magnet toa movable portion of the shipping container latch mechanism; (2)installing a sensing unit proximate to the magnet for detecting changesin the magnetic field profile caused by movement of the latch mechanism;(3) generating a data message containing information about the changesin the magnetic field profile; and (4) transmitting the data message viaa communication network to a control authority.

In one embodiment, a novel apparatus comprises a latch monitor for acontainer door including a magnet disposed on a moving portion of alatch mechanism attached to the container door and an array of magneticsensors disposed in fixed positions relative to a stationary portion ofthe latch mechanism and proximate a path traversed by the magnet when itis caused to move. In another aspect, the apparatus includes a memoryfor storing data provided by the magnetic sensors corresponding torelative positions of the magnet with respect to the array of magneticsensors, and a processor operative according to an executable programfor analyzing the data to distinguish tampering events from a securedindication of the latch mechanism.

In another embodiment, an apparatus for detecting tampering with a latchmechanism of a door of a shipping container, the latch mechanism havinga stationary component and a movable component, comprises an emitter ofelectromagnetic flux disposed on a first component of the latchmechanism; at least first and second sensors, responsive to the flux,disposed on a second component of the latch mechanism; a defined set ofdetection zones proximate the first and second components of the latchmechanism; and a processor configured to receive and analyze outputsignals from the at least first and second sensors to distinguishtampering attempts from authorized or incidental movements among thecomponents of the latch mechanism.

In yet another embodiment a lock detector for a shipping container latchmember having a longitudinal axis and configured to rotate about orslide along the longitudinal axis, comprises an emitter ofelectromagnetic flux having an axis of emission integral with said latchmember and disposed substantially along a radius of said latch member; adetector of the electromagnetic flux comprising at least first andsecond detection elements fixedly disposed proximate said emitter and ona line perpendicular to an axis of emission of the flux, wherein theline lies in the plane of motion of the emitter whether it rotates aboutor slides along said longitudinal axis; wherein the first and secondelements are disposed substantially equidistant on either side of theaxis of emission when the container latch member is in a closed andlatched condition.

In yet another embodiment, a method for detecting movement of a shippingcontainer latch, comprises the steps of attaching a magnet to a movableportion of the shipping container latch; installing a sensing unit on astationary portion of the container latch and proximate to a pathtraversed by the magnet for detecting changes in a magnetic fieldprofile caused by movement of the movable portion of the containerlatch; and processing data representing the changes in the magneticfield profile to determine whether movement of the container latch isauthorized or incidental or a tampering incident. In another aspect, themethod includes the steps of generating a data message containinginformation derived in the processing step; and transmitting the datamessage via a communication network to an external control terminal.

In yet another embodiment, a sensing apparatus for detecting movement ofa shipping container latch, comprises a magnet disposed within the bodyof a movable portion of the shipping container latch; a housing; aplurality of magnetic field sensors disposed in a uniform, predeterminedconfiguration and supported by said housing proximate said magnet, eachsaid sensor providing an output signal proportional to a magnetic fieldintensity produced by said magnet at the location of each said sensor; aprocessor including a memory operating under the control of anexecutable program residing in said memory for receiving and analyzingthe output signal from each sensor to obtain a magnetic field profileproduced by the magnet; and a transmitter for sending a data messagegenerated by said processor, said data message containing informationdescribing the magnetic field profile and whether it comparesidentically with a signature profile stored in the memory.

In yet another embodiment, a method for maintaining a manifest for ashipping container, comprises the steps of reducing the manifest todigital form and storing it in a memory in a central processor;establishing a communication link from the central processor to a latchmonitor installed on the shipping container; transmitting the manifestto the latch monitor for storage in a non-volatile memory segmenttherein; and providing for retrieval of the manifest from a terminalexternal to the latch monitor upon a command transmitted from theterminal to the latch monitor.

In yet another embodiment, a method for maximizing battery life in alatch monitor for a shipping container latch mechanism, comprises thesteps of connecting the output of a battery to a switchmode regulatorloaded by a supercapacitor; coupling each loading circuit in the latchmonitor requiring current to the output of the supercapacitor through alow-loss switch; and controlling the low-loss switch of each circuitaccording to the need for operating current by the circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of the system of the presentinvention;

FIG. 2 illustrates one embodiment of a container yard facility that maybe used by the system of the present invention illustrated in FIG. 1;

FIG. 3 illustrates a container transport and chassis loaded with ashipping container that includes apparatus of the embodiment of thepresent invention illustrated in FIG. 1;

FIG. 4 illustrates a portion of a container door of the shippingcontainer shown in FIG. 3 that includes one embodiment of a latchmonitoring device according to the present invention;

FIG. 5 illustrates a block diagram of one embodiment of electricalcircuitry that may be used in the embodiment of the present inventionshown in FIG. 4;

FIG. 6 illustrates a coordinate diagram of one embodiment of a magneticfield disturbance sensor that may be used in the latch monitoring deviceshown in FIG. 4;

FIG. 7 illustrates a plan view/cross section view of a portion of oneembodiment of a magnetic field disturbance sensor that may be used inthe latch monitoring device shown in FIG. 4;

FIG. 8 illustrates a side view of the portion of the embodiment shown inFIG. 7.

FIG. 9 illustrates a graph of signal outputs from the array 90 ofsensing elements of the embodiment of the magnetic field disturbancesensor shown in FIGS. 6, 7, and 8;

FIG. 10, illustrates one embodiment of a software architecture presentedas a flow diagram for use in the latch monitor 34 of the presentinvention;

FIG. 11 illustrates a flow chart diagram of a communications Task 1process for use in the embodiment of FIGS. 4, 5, and 10;

FIG. 12 illustrates a flow chart diagram of a GPS Task 2 process for usein the embodiment of FIGS. 4, 5, and 10;

FIG. 13 illustrates a flow chart diagram of a sensor Task 3 process foruse in the embodiment of FIGS. 4 through 10;

FIG. 14 illustrates a block diagram of a power system for use in theembodiment of FIGS. 4, 5, and 10;

FIG. 15 illustrates a flow chart diagram of a power management Task 4process for use in the embodiment of FIGS. 4, 5, 10, and 14;

FIG. 16 illustrates a flow chart summarizing a process for maximizingbattery life in the embodiment of FIGS. 4, 5, and 10; and

FIG. 17 illustrates a flow chart diagram of a calibration Task 5 forcalibrating the magnetic disturbance sensor of the embodiment of FIGS. 4through 10.

DETAILED DESCRIPTION OF THE INVENTION

The following description of at least one embodiment of the presentinvention is provided to illustrate and demonstrate the principles ofthe invention. Therefore, this description is not intended to be limitedto the particular embodiment disclosed herein. Persons skilled in theart will understand and appreciate various alternatives to many of thedetails set forth in this description, yet the embodiments realizedthereby nevertheless will fall within and make use of the principles ofthe present invention as recited in the appended claims. As discussedherein above, the present invention addresses the problems ofconventional monitoring and tracking systems and methods for shippingcontainers, whether they are stand alone containers or the box-likecargo enclosures of trucks or other vehicles. These problems include theinability to distinguish movement in mechanisms used for latching andlocking shipping containers that is unauthorized—i.e., tampering—frommovement that is authorized or expected or incidental. The solution tothese problems is provided in the novel invention described as follows.

The invention includes a system, method, and apparatus for detecting theopening of or tampering with the door of a shipping container, truck orvan that utilizes a typical door closure and latching mechanism. Thetypical latching mechanism includes one or more rotating members (a.k.a.rods or bars or poles, and may be termed herein rotating rod or bar,latch rod, locking bar, etc.) attached to the outside of the doors ofthe container. A lever attached to the rotating member enables one tolatch and lock the door. The door may be unlatched by lifting androtating the lever through an angle away from the door. The presentinvention employs analog sensing technology to measure and detect thedegree of rotation or extent of longitudinal movement of the rotatingmember when the lever is moved or the rotating member is otherwisecaused to rotate or shift in position. The analog approach provides muchmore information that can be analyzed and interpreted to distinguishbeyond a simple either/or condition that is often amenable to falseindications. The invention is also capable of detecting other kinds ofevents that are evidence of tampering attempts, or of incidentalcircumstances that, while not tampering attempts per se, may affect theoperation or integrity of the apparatus of the present invention. Forexample, the use of a magnetic field external to the structures of theinvention, which may indicate an attempt to disable or trick theapparatus into allowing a container door to be opened by an unauthorizedagent, is detectable and may be logged in the apparatus. In anotherexample, natural or incidental events such as electromagneticdisturbances from weather events or man-made circumstances may also bedetected and logged, or ignored.

In one embodiment, the detection system includes a latch monitor to bedescribed that employs a magnetic field disturbance detector. A smallbut powerful magnet, such as a bar magnet having a north and a southpole, is attached to or embedded in the rotating member of the latchmechanism. The magnet establishes a magnetic field in the vicinity ofthe magnet. In a tamper-proof box or housing installed next to therotating member is located an array of very small, analog magnetic fieldsensors that provide a sensitive way to measure and characterize theprofile of the magnetic field, in both its extent and intensity, in anypossible condition of the container latch mechanism whether it isstationary or non-stationary. The box or housing, which houses a controlunit and transceiver, contains a processor, receiver-transmitter, andantenna in addition to the magnetic sensor array. The processor receivesand processes output signals from the sensors. The receiver-transmitterand antenna enables communication between the latch monitor and externalentities such as a base station, server, or nodes of a mesh network gridestablished in a container yard, for example.

When the container door is latched, the processor in the latch monitorevaluates the characteristics of the sensed magnetic field and stores itas a signature or “fingerprint.” Any attempt to use the latch mechanism,or any movement of the rotating portion of it, causes movement of themagnet, which disturbs the field. The altered field characteristic iscompared to the “fingerprint” by the processor. The mismatch isdetected, stored or logged, and interpreted within a user-selectableamount of variance to reduce false alarms or alerts. The processor inthe latch monitor described herein further contains software tointerpret the disturbance of the magnetic field produced by the magnetin the rotating or moving portion of the latch mechanism to distinguisha bonafide container breech from accidental or incidental disturbances.Such disturbance events may include vibration caused during handling,transit, or movement of the container in authorized actions. Whennecessary, according to a pre-established protocol, an alert signal maybe output to a communication network and a message transmitted to anauthority for response when the variance is exceeded.

While the foregoing example is implemented based on a magnet and amagnetic sensing system, the invention contemplates other types ofelectromagnetic field emission devices including electromagnets, lightemitters, etc., and appropriate corresponding sensing systems.Accordingly, as will be described in detail herein, the presentinvention provides new and heretofore unavailable functionalcapabilities in tracking and monitoring devices for shipping containers,providing far beyond the limited functions of conventional passive oractive RFID “Tags,” for example. The present invention includes advancedsensing apparatus for detecting movement of latch mechanism components,and processing and communication apparatus for interpreting theconditions detected by the sensing apparatus, logging the events, andcommunicating the events as necessary to external authorities. Thepresent invention further includes the ability to store and processrequests for an electronic manifest to accompany the shipping containerthat is available for review as necessary by shipping facilities andcustoms or security personnel.

Referring to FIG. 1, there is illustrated one embodiment of the systemof the present invention. A shipping container yard system 10 (“system”)that is typical of an intermodal shipping facility is shown thatincludes a yard server 12 and a connection to a global communicationnetwork such as the Internet 14, to which may also be connected a systemoperations facility 16. The foregoing components of the yard system 10may further be part of a larger scale logistics and shipment trackingand management system. It will be apparent that standardization ofequipment and protocols is essential to the operating efficiency andsecurity of such interconnected systems. A logistics database 18 and atracking database 20 may also be connected to the yard server 12. Theyard server 12 may further be in communication with additional unitssuch as a gate operations terminal 24, a smart phone or tablet PC(“handheld terminal”) 28, or a base station 42. The handheld terminal 30may be a personal digital assistant or PDA (as shown), or alternativelya smart phone or a phone configured for wireless application protocol(WAP). The gate operations terminal 24 may include a PC 26 incommunication with the yard server 12. The base station 42 may beconfigured as a small vehicle to provide a mobile base station 44 thatincludes a communication terminal 46 coupled to an antenna 48 via atransmission line 50.

The mobile base station 44 may be in communication with a shippingcontainer 22, which may or may not be supported on a chassis 40 of atruck. In the present example of the invention, the mobile base stationis shown in communication with a latch monitor 34 of a latch assembly ormechanism 32, which includes the latch monitor 34 attached to a door 52of the shipping container 22, and a rotating latching rod 36 operated bya handle 38 attached thereto. The container door 52, rotating rod 36,and handle 38 illustrated and described is typical of a standardconfiguration. Generally, two doors are used on each container. Bothdoors are equipped with the same latch mechanism 32 as described above.As will also be apparent, the latch monitor 34 of the present inventionmay be installed on either door 52 of the container 22, and at anylocation along the rotating rod 36 except where the handle 38 isattached. As will be further described for FIG. 4 herein below, thelatch monitor 34 includes a magnet installed in or on the latching rod36 adjacent the position of the latch monitor 34. In some containerlatch assemblies the latching rod or bar may be configured to slidelinearly along its longitudinal axis rather than or in addition torotating about the longitudinal axis.

Referring to FIG. 2 there is illustrated one embodiment of a containeryard facility 60 (“yard 60”) that may be used by the system 10 of thepresent invention illustrated in FIG. 1. The yard, which may be situatedon available land, includes an entrance 62, a gate house 64, and alog-in booth 66. The gate house 64 may include a canopy or be anenclosed space. Similarly, the log-in booth 66 may be a fully enclosedoffice. The yard 60 may include container spaces 68 designated for thestorage of containers 22 and chassis spaces 70 designated for thestorage (i.e., parking) of truck chassis 40 as shown in FIG. 1. Thecontainer spaces 68 typically accommodate the stacking of containers tomaximize the utilization of the available space. The container spaces 68may be designated by lot identification symbols such as the letters W,X, Y, and Z as shown in FIG. 2. The chassis spaces 70 enable storage orparking of chassis 40, with or without a container 22 attached thereto.The chassis spaces 70 may also be designated by lot identificationsymbols such as the letters A, B, C, D, and E as also shown in FIG. 2.In some yards 60, the spaces 68, 70 and/or the individual spaces withinthe lots may have coordinates of latitude and longitude associated witheach space, to enable accurate location information for each container22 stored therein. One or more mobile base stations 72 may be used, toroam the yard while communicating with the latch monitor systems 32 andthe yard server 12, which is typically located in a yard office 74. Insome embodiments, the base station(s) 72 may be located in the yardoffice 74. The yard 60 is merely one example to illustrate exemplarybasic content of a container yard for use with the present invention.Many variations are possible to adapt to local circumstances.

Referring to FIG. 3 there is illustrated a container transport vehicle80 (a.k.a. “Truck 80”) and chassis 40 loaded with a shipping container22 that includes the apparatus of the described embodiment of thepresent invention illustrated in FIG. 1. The same reference numbers areused as in FIG. 1, which refer to the same structures. For example, thecontainer 22 includes left and right container doors 52 secured in aclosed position by a set of vertically disposed rotating rods 36,usually two such rods 36 for each door 52. The rotating rods 36, whichfunction as locking bars, operate to release locking cams (not shown inthe figure because they are well known standard features of the lockingbars) at the top and bottom of the locking bar 36 when it is rotated bya lever or handle 38.

FIG. 4 illustrates a portion of a container door 52 and the door latchassembly or mechanism 32 of the shipping container 22 shown in FIG. 3.The door latch mechanism 32 includes the rotating latching rod 36, itshandle 38, 82, the bracket 84, and the magnetic disturbance sensor 88,90 and its associated components to be described. The drawing of FIG. 4includes one embodiment of a latch monitor 34 according to the presentinvention. The latch monitor 34, which may be enclosed in a housing 35,is shown positioned to the right of and near the rotating latching rod36, as would likely be the case for mounting on the right hand containerdoor 52. A mirror image drawing of FIG. 4 would show the orientation ofthe latch monitor 34 and rotating rod 36 for a mounting installation onthe left container door. Several essential features of the latch monitor34 are shown including a first angular position of the handle 38 of therotating rod 36 extending outward from the surface of the door 52 andparallel with the axis of the bar magnet 88. This angular position ofthe handle 38 corresponds to an unlatched condition of the door latchmechanism 32. A second angular position of the handle 82 is shown inphantom (and again, parallel with the axis of the bar magnet 98) inplace within a bracket 84, corresponding to a latched condition of thelatch assembly or mechanism 32. In the description that follows, themagnet will be designated as magnet 88 unless otherwise stated. Themagnet 88 is shown in this example as a small cylindrical bar magnetoriented along a radius line of the rotating rod 36. The bar magnet 88may be generally oriented perpendicular to a longitudinal centerline ofthe rotating rod 36. It will often be the case, for example, that themagnet 88 will be oriented approximately parallel with the handle 38 ofthe rotating rod 36.

One of the novel features of the present invention is the ability of thelatch monitor 34 to distinguish between tampering with the latchmechanism 32 and authorized or incidental movement of the components ofthe mechanism relative to each other. Selection of the magnet 88 for thelatch monitor of the present invention is an important factor in thedesign. The magnetic flux required of the magnet 88 falls within arelatively narrow range, depending on the proximity of the sensors 91-94to the magnet 88, the sensitivities of the sensors, the resolution ofthe measurements required to detect and differentiate the variations indisplacement of the components of the latch assembly 32, etc. As will bedescribed, if the flux is excessive in the vicinity of the measurement,the detection zones—defined adjacent areas through which the magnet 88moves relative to the sensors in the sensor array 90 (which may also becalled an array of sensors 90 herein)—cannot be clearly resolved.Conversely, if the flux is weak in the vicinity of the measurement,reliable detection cannot be assured. Either condition results inambiguous measurements that are not adequate for distinguishingtampering from authorized or incidental movement of the latch mechanism32. Reference to the sensitivity specifications of the sensors, and tothe geometry and dimensions of the magnet and sensor relationships asthe latch mechanism 32 is operated through its range of motion, providethe conditions necessary to determine the required sensitivity. Thegeometry and spatial relationships of the sensor array 90 and the magnet88 will be described further in conjunction with FIG. 6.

Continuing with FIG. 4, a suitable magnet for the magnet 88, availableas a standard item from CMS Magnetics, Richardson, Tex., is a bar magnetmade of Neodymium, Iron, and Boron (NdFeB), having dimensions (in thisexample) of 0.125 in. dia.×0.500 in. length, a flux density (or energyproduct) of 42 MegaGauss-Oersteds, and a surface field strength of 4140Gauss. The surface field strength is an important parameter because itis the flux at the end of the magnet 88 (i.e., in close proximity to thepole of the magnet) that is detected and measured by the array ofsensors 90. This material NdFeB is selected because it retains itsmagnetism longer (high coercive force) than other materials, even in thepresence of a strong demagnetizing field, and because the materialprovides a much stronger field per mass unit. The magnet may be nickelplated and/or embedded in the rotating rod within a non-magnetic sleeve86, 96 of brass or aluminum to protect the magnet from corrosion ordamage. The end of the magnet 88, 98 proximate the sensor array 90 willpreferably be flush with the surface of the rotating rod 36. The latchmonitor 34 should be mounted on the container door 52 so that theproximate pole of the magnet 98 is as close to the sensor array 90 aspossible. In a practical sense, this closeness will limited by thethickness of the housing of the latch monitor 34 to approximately 0.150inch.

The orientation of the array of sensors 90 in FIG. 4 is appropriate formounting the latch monitor 34 adjacent to the right side of the rotatingrod 36 as shown. Alternatively, the latch monitor 34 may be configuredwith the array of sensors 90 on the opposite side of the latch monitor34 so that it may be mounted adjacent to the left side of the rotatingrod 36. Further, some embodiments may be configured to accommodatepositioning of the latch monitor 34 on either side of the rotating rod36 merely by inverting the orientation of the latch monitor 34 next tothe rotating rod 36.

The magnet 88 is attached to the rotating rod 36 (alternatively “bar 36”or “pole 36”) portion of the container latch assembly 32 so that it isadjacent to the sensor array 90 when the rotating rod 36 is in a closedposition 82. The closed position 82 is indicated by the phantom drawingof the handle 38 within the bracket 84. The bracket 84 may includefeatures to facilitate locking the handle 38 into the closed position82. The magnet 88 establishes a magnetic field in its vicinity, which,when undisturbed, exists in a quiescent form having an extent and anintensity that is measured by the sensor array 90 and processor 100. Thesensor array 90 detects the direction and intensity of the field at thelocation of each sensor 91-94. As will be described in detail hereinbelow, the combination of the data from each sensor location enables theprocessor 100 to map or create a graph of the profile of the magneticfield.

Briefly, the profile of the magnetic field in this quiescent condition—asignature or “fingerprint” comprising the combination of the signalsfrom the array 90 of sensors—is converted to digital data and stored ina memory device within the latch monitor. If the rotating bar 36 onwhich (or in which, in this example) the magnet 88 is mounted is moved,the profile of the magnetic field is changed or “disturbed.” The changedprofile is compared with the stored “fingerprint.” This comparison isperformed at frequent periodic intervals, providing what is essentiallya continuous monitoring of the magnetic field established by the magnet88. If the differences in the profile are not due to normal vibration orother conditions not involving intentional movement of the latchmechanism 32, the processor (or CPU) 100, which interprets thedifferences according to stored algorithms, then the processor 100 maygenerate an alert signal that is output to the transmitter portion ofthe transmitter/receiver (Tx/Rx) 106 for communication via antenna 108to a mesh communication network linking the latch monitor 34, basestation 42, yard server 12, and any other latch monitors 34 (or nodes)in the vicinity, signifying that the container has been tampered with.The latch monitor 34 may alternatively be polled periodically to accessa “log” stored in memory 104, for retrieval of the profile datarepresenting the condition of the latch mechanism 32.

Continuing with FIG. 4, other elements of the latch monitor 34 as shown,such as the sensor array 90 having sensors 91-94 (only sensors 91 and 92are shown in FIG. 4), and internal processor circuit components 100,102, 104 of the latch monitor 34. The processor circuits include amicroprocessor 11, an analog-to-digital converter 102, and a memory 104,which may further include a 4K EEPROM, a 256K FLASH memory, and an 8KSRAM. The EEPROM may typically contain stored or user-setable parametervalues, threshold and time values, reference and state levels, etc. TheFLASH memory may typically contain logged events files (time, location,event descriptors) and electronic manifest data. The SRAM may containglobal variables for any of the tasks and keep track of the latestreading during the GPS task.

Also shown in FIG. 4 is a status monitor circuit 118 that includes anarray of LED (light emitting device) lights A (120), B (122), C (124),and D (126). The status monitor 118 and the operation of the LED lightsA, B, C, and D (“LEDs”) will be further described in conjunction withFIG. 5. Further, other internal components of the circuitry within thelatch monitor 34 will be described further in conjunction with FIG. 5.

One suitable magnetic field sensor for each of the sensors 91, 92, 93,and 94 of the sensor array 90 is a type A139X Micropower 3 Volt LinearHall Effect Sensor available from Allegro Microsystems, Inc. ofWorcester, Mass. 15036. This device has a sensitivity of 1.25 mV/G,tri-state output, and a sleep mode to conserve battery energy. It isalso, because of its very small size, well-adapted to use in an array ofa plurality of like sensors. As will be described further for FIG. 6,the four sensors 91-94 are arranged in a single row, laterally disposedwith respect to the vertical axis of the rotating rod 36, and positionedsuch that the north (or south) pole of the magnet 88 may be centeredbetween the sensors 92 and 93 when the latch mechanism 32 is in a closedand latched condition. Movement of the magnet 88, corresponding tomovement of the handle 38 as the latch mechanism 32 is opened or closed,thus swings in an arc in the same plane as the sensors 91-94. The planeof motion of the magnet, which plane includes the array of sensors 90,is divided into a series of detection zones to enable correlation of thesensor outputs with the positions of the magnet 88. See FIGS. 6 through9 herein below.

During development of the magnet and sensor array for the latch monitor34 of the present invention, experiments with a number of differentsensor arrays, and the number of sensors in the array, were performed todetermine which one provided the least ambiguous measurements of thefield associated with the magnet as it moved through its arc of motionwhen the latch mechanism was opened and closed and latched. In addition,the conditions of movement of the components of the latch mechanism mustbe defined for tampering events as well as for authorized or incidentalevents involving the relative movement of the magnet with respect to thesensing apparatus. One would think that the array of sensors required todetect and characterize all relevant positions of the magnet in therotating rod of the latch mechanism must include at least two sensorsdisposed along each of two orthogonal axes in a plane, wherein the planecontaining the sensing elements is disposed parallel with thelongitudinal axis of the rotating rod and perpendicular to the axis ofthe bar magnet when the latch mechanism is closed and latched. However,unexpectedly, it turned out that the best combination of sensingelements is an array of four elements disposed along a straight line inthe plane of rotation of the magnet and spaced close to the proximateend of the magnet when the latch mechanism is closed. In thisrelationship the line of sensing elements is perpendicular to the magnetaxis when the latch mechanism is closed. The surprising result was thatthis simple geometry enabled reliably distinguishable measurements ofthe movements of the magnet in a three dimensional rectangularcoordinate system. This geometry will be further described for FIGS. 6through 10 herein below.

Continuing with FIG. 4, a suitable selection for the processor (CPU) 100in this example is a type ATmega2560 available from Atmel Corporation,San Jose, Calif. The ATmega 2560 is a low power 8-bit microcontrollerwith RISC architecture, several non-volatile memory segments, a 10-bitanalog-to-digital converter (ADC), and other features that provide verylow power consumption. This microcontroller thus includes the processor100, A/D 102, and memory 104 in a single chip. A suitable candidate forthe transmitter/receiver 106, which has location capability and a builtin processor, is a type CC2431 Low Power RF SOC (system on chip)developed for so-called “Zigbee®” wireless network applications andavailable from Texas Instruments, Dallas, Tex. Persons skilled in theart will readily understand how to configure these components to performthe functions required to implement the present invention as set forthin the following description. Generally, protocols must be defined foruse in a peer-to-peer or mesh network, wherein the “clients,” orterminals (i.e., latch monitors and base stations, etc.) are defined as“nodes” in the network. In the network of the present invention, theclients are power-conscious units in which the radio or transceiver 106is only powered on at periodic or certain controlled times. Usefulreferences for configuring the mesh network include Application NoteAN042, Rev. 1.0, “CC2431 Location Engine,” by K. Aamodt, published byTexas Instruments, Dallas, Tex. and incorporated herein by reference inits entirety; and a data sheet for the CC2431, Rev. 2.01 (SWRS034B)“System-On-Chip for 2.4 Ghz ZigBee®/IEEE 802.15.4 with Location Engine,”also available from Texas Instruments, Dallas, Tex., and incorporated byreference herein in its entirety. The ZigBee® wireless network standardis available from the ZigBee® Alliance at www.zigbee.org.

Communication between the transceiver 106 in the latch monitor 34 andother nodes in the network—base station, gateway (server), etc.—proceedsaccording to a standard protocol, summarized in the following paragraphsdescribing FIG. 5.

FIG. 5 illustrates a functional block diagram of one embodiment ofelectrical circuitry that may be used in the embodiment of the presentinvention shown in FIG. 4. The latch monitor circuit 128 for the latchmonitor 34 includes the aforementioned Hall Effect Sensor (HES) array 90coupled to the processor 100 at the inputs to an analog-to-digitalconverter (A/D) 102 section of the processor 100. The processor or CPU100 includes in its memory 104 several segments such as EEPROM, SRAM,and Flash memory for storing instructions and algorithms, loggingoperating event data, and storing other data such as latch monitor data,container manifest information, etc. For example, in the illustrativeembodiment, the internal Flash memory may hold program as well as theevent logs to be described. Further, it is also possible to configurethe system to utilize external non-volatile memory such as SD memorycards, portable hard disc drives, and the like for the storage of logevents or other data.

Also connected to the CPU 100 is a silicon serial number chip (SSN) 101.The SSN chip 101 provides a unique identifier that may be accessed via aserial connection. It is provided in the latch monitor 34 to enable eachlatch monitor to be uniquely identified on a global basis for anextended period of time (for example, up to twenty years). A shippingcontainer 22 bearing the latch monitor 34 moves within, among, andbetween various infrastructure zones, ports, and yard systems 10,countries of the world, different tracking systems, as these shippingcontainers move via air, land, and sea transport vehicles or are storedawaiting further operations. Although it may seem that fieldprogrammable identification numbers would be suitable for a latchmonitor for shipping containers, experience suggests that the likelihoodof duplicate numbers or misplaced identifiers, though small, should beavoided. Thus, it is essential that no two latch monitor devices havethe same identification number. In the present embodiment, the SSN chip101 is also selected to be independent of whatever radio technology ischosen for the communications functions of the latch monitor 34 embodiedin the transceiver 106. Since the transceiver device selected for thetransceiver 106 in some present or future applications may employ one ofseveral available technologies, or perhaps employ multiple radiotechnologies, each possibly having a serial or identification memberingsystem, it is important that the latch monitor 34 have a unique,independent identifier. The SSN chip 101, as implemented in theillustrated embodiment, provides a unique 48 bit member (a Global UniqueID) stored in a one wire, serial ROM that identifies the particularlatch monitor to whatever communication or tracking or managementnetwork to which it may be connected. The SSN is accessed during a POST(power on self test) routine to be described herein below. The SSN chip101 employed in the illustrated embodiment is available as an integratedcircuit from Maxim/Dallas Semiconductor, Richardson, Tex. as part no.DS2401.

One of the important features of the present invention is the provisionof sufficient storage capacity to store the manifest for the containerin the latch monitor 34 attached to the container 22. As is well known,a manifest is a listing of the contents of a container or transportvehicle. The information in a manifest includes details of the contentsand its value, the origin, shipper and destination, etc. The manifestinformation, reduced to digital form and stored in the memory ordatabase of a processor at a shipping point, for example, may then betransmitted to the latch monitor 34 for storage therein in a segment ofits non-volatile memory 104. This manifest is retrievable for viewing oncommand by shipping or security officials or by U.S. Customs officialsat any point during transit. Moreover, a complete and functioningnetwork between local servers is not required to retrieve the manifestinformation. It is only required to be within range of other nodes inthe communication network.

The manifest data, electronically stored in the latch monitor(downloaded) at the point of origin, may be uploaded to a base stationor other authorized terminal whenever the container comes within rangeof the base station and viewed on a yard server display, or,alternatively, a mobile base station comes within range of thecontainer, with viewing enabled on a yard server display. The manifestmay also be viewed on handheld devices in communication with the yardserver. However, as a security measure, it is not advisable to includedirect upload of the electronic manifest to a handheld device exceptwhen it is being operated by Customs or security officials. The latchmonitor 34 includes support for the e-Manifest of the AutomatedCommercial Environment (ACE) protocol, a commercial trade processingsystem recently developed by the U.S. Customs and Border Patrol (“CBP”).The CBP is a component of the Department of Homeland Security. Thus, itis also possible that the e-Manifest can be automatically uploaded tolocal CBP computers for compliance with the ACE system.

As an example of downloading an electronic manifest from the latchmonitor 34, the process e.g., so-called “flash update,” occurs duringcommunication with the latch monitor 34 via its transceiver 106according to the communications protocol embodied in the transceiver 106and the network to which it is connected. The communication network maybe implemented by any of a variety of radio or wireless configurations.In this illustrative example, a ZigBee® “mesh” system is employed. Inthis communication, messages are exchanged between the sender andreceiver (respectively, e.g., a “tower” or yard office and a latchmonitor on a shipping container) to begin a message sequence,acknowledge it, clear and acknowledge a checksum, send and check a blockof data, repeating the latter step until all the blocks in the sequenceare sent, checked, and acknowledged. This process is well known topersons skilled in the art and need not be explained in detail herein.The process for uploading data from the latch monitor on command to abase station or yard office or other terminal is similar but in thereverse direction. These communications processes are made possible bythe fact that the latch monitor is an intelligent, active device, byvirtue of the processing, storage, and communicating capabilities builtin to it, along with the latch monitoring capabilities included withinthe latch monitor 34.

The CPU 100 is the central processor in the latch monitor 34, runningsoftware that controls all functions of the device including wirelesscommunication, sensor monitoring including processing (A/D 102) of theanalog signals from the Hall Effect Sensors, location detection, powermanagement, memory management, time keeping, and status display, as willbe described. Criteria for selecting the CPU include low powerconsumption and judicious use of power saving modes, on-chipnon-volatile memory segments, A/D conversion, real time clock, etc. Asuitable choice is the 8-bit type microcontroller mentioned hereinabove. A more efficient choice is a microcontroller that enablessampling and storing the samples for later analysis by the processor,rather than performing the analysis in real time, which requires theprocessor to be awake during the sampling operations. This distinctionwill be described further for FIGS. 15 and 16.

The processor or CPU 100 is coupled to a transceiver 106 forcommunicating via antenna 108 with other nodes in a wireless network(See FIGS. 1 and 2) of shipping containers equipped with the intelligentlatch monitors 34 according to the present invention, base stations 42,and the “backend system” or central office yard server 12. Thetransceiver 106 in the exemplary embodiment described herein performscommunication reception and transmission under the control of the CPU100 and, in this embodiment, autonomously functions as a mesh routerforwarding packets on behalf of other client functional units in thelatch monitor circuit 128. The transceiver 106 (also known as the“Zigbee® radio 106”) is coupled to an internal antenna 108 in theillustrated embodiment. In other embodiments, an external antenna may beused. The choice of technology for the radio communication function ofthe latch monitor 34 is not confined to the ZigBee® system or to the useof a mesh type network. Other systems and protocols may be employed.Further, in future embodiments, it is possible, and may be advantageousto employ multiple radio technologies (e.g., ZigBee®, 900 MHz, UWB,cellular, or others).

Continuing with FIG. 5, the latch monitor circuit 128 further includes apower supply and controller section 110 (“power supply 110”). The powersupply 110 includes a battery (not shown but enclosed within the latchmonitor unit 34) that supplies current to all of the subsystems in thecircuit 28. The battery in the illustrative example may be a lithium iontype providing nominally 3.6 volts DC. The power supply 110 is monitoredand regulated under the control of the CPU 100 to maximize the life spanof the battery. Algorithms implemented in the software turn off theindividual subsystems in the latch monitor circuit 128 when they are notin use. Further, the supply voltage is monitored so that a condition oflow power, or an intrusion event, for example, will enable the latchmonitor 34 to transmit an alert or other message via an alert sequencebefore the power supply expires. Further details of the power supply 110and its power management functions will be described in regard to FIGS.14, 15, and 16.

The circuit 128 of the latch monitor 34 further includes a real timeclock 112, a GPS (Global Positioning System) receiver 114, and a motionsensor 116, all coupled to the CPU 100 to utilize or control theirrespective functions. The real time clock 112, which is read and writtento as necessary, provides timekeeping in the event that the GPS receiver114 is unable to lock onto satellite signals. The GPS receiver 114 usedin this illustrative example may be the type SiRF GSC2x GPS chipsetavailable from USGlobalSat, Inc., City of Industry, Calif. 91745, anaffiliate of Globalsat Technology Corporation of Taipei, Taiwan. As iswell known, a GPS receiver functions to determine the latitude andlongitude coordinates of the GPS receiver 114. Software running on theCPU 100 queries the GPS receiver 114 using algorithms to accuratelydetermine the location of the latch monitor 34 and the container towhich it is attached.

The motion sensor 116 in this example is a so-called “at rest” devicethat detects physical movement or vibration of the unit in which themotion sensor is incorporated. Information provided by the motion sensor116 may be used as part of a routine to awaken the CPU 100 or othercircuits, or to provide an input to a tampering detection program. Thissensor 116 is a passive device that functions as a normally closedswitch when at rest, then opens when disturbed. A suitable component isa type SQ-SEN-200 available from SignalQuest, Inc. of Lebanon, N.H.03766. In operation, a gentle disturbance will result in one or moreshort duration “opens.” A more aggressive jolt results in much longeropen periods. Software running on the CPU 100 determines when suchphysical movement or disturbance begins and ends, and determines theseverity of the motion. For example, if the disturbance exceeds athreshold for duration or magnitude, or both, an “in motion” state willbe detected and the CPU then signals the movement event to an eventlogger in the CPU 100.

Continuing further with FIG. 5, the circuit 128 of the latch monitor 34includes a status indicator 118 that may report certain calibration,operational (e.g., a “heartbeat”), and diagnostic routines or conditionsin process or previously logged. An array of LED lights S1, S2, S3, andS4 (“LEDs”), respectively given reference numbers 120, 122, 124, and 126and driven and controlled by the CPU 100, is coupled to the statusindicator 118. The LEDs 120-126, though controlled by the CPU 100 may beenabled or disabled via commands initiated by the backend 12 (“yardserver”) software and sent via the wireless interface. In oneillustrative embodiment (See FIG. 4), the LEDs may be programmed asfollows: LED “A” turns ON when a radio communication is in progress; LED“B” turns ON when the GPS function is active, blinking with eachsentence received; LED “C” turns ON when a sensor reading is beingperformed; and LED “D” turns ON when there is a power measurementpending or in progress. Each respective LED turns OFF when the operationof the function is completed. The LEDs may be operated in several modes,including OFF, ON, or blinking. An LED that is ON may have theappearance of being DIM (a rapidly blinking mode, with a repetition rateof approximately 10 Hz) or BRIGHT (a continuously illuminated LED). Inthis description, an LED that is ON is assumed to be ON continuouslyunless otherwise specified.

The individual functions of the LEDs is described as follows. LED A(120) corresponding to task one (1), communications monitor, will be ONdimly (e.g., blinking at a 10 Hz rate) when the unit is attempting toestablish a communication link with a base station or a back endstation. LED A (120) blinks OFF when transmitting, then becomes ON whilelistening for a reply from a base station. For example, when a latchmonitor 34 comes within range of a base station 42, LED A (120) will“wake up” in a dim ON state as it tries to join, i.e., “associate,” withthe personal area network (PAN), then blink OFF (only for about one-halfsecond) during the brief time it transmits a “check in execute packet,”(lock to base), then turn ON while listening for a reply from the basestation, then, blink a few times (LED OFF to transmit the next packetand then ON to await the reply, for however many packets are needed),then turn OFF, indicating that the base station has completed thecurrent transaction with the latch monitor 34 and allowed it todisconnect.

LED B (122) corresponding to task two (2), GPS monitor, blinks in timeto the reading of GPS strings from the GPS receiver 114 in the latchmonitor 34. After obtaining valid coordinates, the blinking cadence willchange slightly so that it appears to be ON more often, indicating avalid “fix.” Additional readings will follow for approximately 30seconds, or for a period sufficient to improve the resolution of thecoordinate values.

LED C (124) corresponding to task three (3), sensor monitor, becomesilluminated ON when a sensor reading is initiated and turns OFF when thereading is completed. This LED is ON only when a sensor reading istaking place. The duration of time it is ON indicates whether the dooractually opened (time=2 seconds) or whether the reading indicates a doorclosed or a “jiggle,” i.e., a false open reading (time=one second).Also, during the power on self test sequence (POST), this LED 124 maybegin indicating the blink codes for the POST after the latch monitor 34completes the boot up cycle.

LED D (126) corresponding to task four (4), power management, isilluminated to indicate monitoring battery levels during this task. Itis ON dimly during the period when the latch monitor is waiting to takea power measurement. The sequence does not operate continuously but atintervals to save power. The interval timing is controlled by aparameter called “Power Supply Access Time” (PAST).

The LED blink codes are produced on the LEDs A-D immediately after thePOST routine has completed. The blink codes may also be presented upon areset event, in which case an abbreviated POST may be run. In thisillustrative example, three sets of LED ON codes are displayed in asequence, each set illuminated for approximately 400 milliseconds (ms),and each set separated by a 100 ms interval in which all LEDs are ON 50ms and OFF 50 ms. Following the third (last) set, all LEDs are OFF forapproximately 1500 ms. The indications of the blink code sets aredefined in the order of LEDs A; B; C; and D. Thus, the first set ofblink codes, when ON for 400 ms indicates respectively: data flashfails; GPS fails; (reserved); and (reserved). The second set of blinkcodes, when ON for 400 ms indicates respectively: SSN (silicon serialnumber) read fails; Zigbee fails; sensor fails; and power monitor fails.The “SSN” is a unique 48 bit member (a Global Unique ID) stored in a onewire, serial ROM that identifies, during the POST routine upon start up,the particular latch monitor to whatever network it may be connected to.It is available as an integrated circuit from Maxim/DallasSemiconductor, Richardson, Tex. as part no. DS2401. The third set ofblink codes, when ON for 400 ms indicates respectively: RTC (real timeclock) power loss; RTC not running; (reserved); and, internal flashfails. These blink codes enable the installer or technician to identifyfunctional problems with the latch monitor 34 reported during the POSTroutine. If three quick blinks occur with nothing in between them, allsections of the latch monitor circuit 120 are functional.

The array of LEDs 120-126 may also be used during a calibration sequence(to be described) that is performed when the latch monitor 34 isinstalled on a container 22 or reset following an unauthorized orincidental event affecting the sensor operation. For example, the row ofLEDs 120-126 may be energized to flash rapidly in one direction toindicate to an installer to open the container door, and flash in theopposite direction to indicate or instruct the installer to close andrepeat the open/close door sequence several times to enable the latchmonitor circuit 128 to record minimum/maximum values for all of thesensors in the sensor array. Further, the sensor LED may be energized toflash or blink during a period of calibration for the latch monitor toestablish a “neutral” door open zone, as will be described.

FIG. 6 illustrates a rectangular coordinate diagram 130 of oneembodiment of a magnetic field disturbance sensor for use in the latchmonitor 34 shown in FIG. 4. The coordinate system 130 includesorthogonal axes x, y, and z (respectively 132, 134, and 136), the magnet98 positioned along the positive x axis 132 with its north pole locatednear the origin and the south pole proximate the sensor array 90. Thesensor array 90, including the sensors 91, 92, 93, and 94, is shownaligned in a straight line or a geometrical tangent disposed parallelwith the z axis 136. The center point of the array, midway between thesensors S1 (92) and S3 (93) and designated in the figure as zero degrees(0°), is aligned along the x axis 132, just beyond (in a positivedirection) the south pole of the magnet 98. Although the sensor array 90is shown as an assembly of sensors on a planar member designated as thesensor array 90, the planar member is shown in this embodiment torepresent that the individual sensors 91-94 are in a fixed relationshipwith each other within the latch monitor 34. In an alternate embodiment,it is possible to arrange the sensor array 90 along a curved line orarc, wherein the arc is within the same plane as the rotation of themagnet 88 and the radius of the arc rotates around a center along the xaxis, as if the sensor array 90 were bent into an arc that turns theends of the sensor array 90 inward toward the origin of the x, y, and zcoordinates.

The y axis 134 corresponds to the axis of rotation of the rotating rod36 of the latch mechanism 32. The magnet 98, when the rotating rod 36 isrotated, will be caused to move in the x-z plane (represented by the xaxis 132 and the z axis 136) of FIG. 6, generally within the quadrantbounded by the positive x 132 and z 134 axes. Such movement correspondsto the normal range of motion while opening and closing the latchmechanism 32. Motion in the direction of the negative x 132 and z 134axes may be incidental or evidence of tampering. Motion in the directionof the positive or negative y axis 134 may correspond to incidentalmovement or the latching mechanism. One example of incidental motionalong they axis 134 is vibration of the shipping container 22 and/orlatch mechanism 32 during movement of the shipping container 22 and maytypically be ignored. Such motion in they axis direction will bereflected in reduced amplitudes, but exhibit the same zone data profileas the signatures. Motion in the minus x direction will typically bereflected as a weakened profile. Another example of apparent signalvariation along the negative x axis may indicate an attempt to interferewith the magnetic field in the space between the magnet 88 and thesensor array 90. As will be apparent, the sensors 91-94 are positionedto sense the intensities of the magnetic field produced by the magnet 88(98) at the respective sensor locations. Motion in the z axis directionwill typically be reflected in a change in the profile and may beevidence of tampering. One such example is an attempt to rotate thelever 38 of the rotating rod 36 away from its closed and latchedposition. The resulting pattern or signature of the Field strengths fromthe set of magnets is interpreted according to algorithms applied to thesensor measurements by the CPU 100 in the latch monitor circuit 120 ofFIG. 5.

Referring to FIG. 7 there is illustrated a plan view/cross section viewof a portion of one embodiment of the magnetic field disturbance sensorthat may be used in the latch monitoring device 34 according to thepresent invention. This view is downward along they axis, from thepositive end toward the negative end of they axis, coincident with theaxis of rotation of the rotating rod 36. The outer surface of therotating rod 36 is shown coincident with a semicircle centered on theaxis of rotation (i.e., they axis) of the rotating rod 36 and rangingfrom a minus 90 degree (−90°) angle through a zero (0°) degree referencealigned with the center of the array of sensors 90 to a plus 90 degree(+90°) angle. It will be noted that the axis of rotation of the rotatingmember (the rotating rod 36 in this embodiment), the zero degreereference, and the center of the sensor array 90 are aligned along asingle straight line. Also shown are the container 22 and the latchmonitor 34 attached to a door 52 of the container 22 as shown in FIGS.1, 3, and 4. Included in the drawing are the relative positions of thesensors S1 (91), S2 (92), S3 (93), and S4 (94) with respect to therotating rod 36 and the magnet 88 embedded therein. As describedpreviously, the magnet 88 in this embodiment rotates through an arc whenthe rotating rod 36 is rotated between a closed position at zero degrees(0°), with the magnet 88 shown as magnet 88A in phantom and aligned withthe 0° reference, and an open position in which the magnet 88 is shownas magnet 88B in phantom and aligned with the −90° angle. In another,mirror image embodiment, when the latch monitor 34 is installed on theopposite side of a rotating rod 36, the rod 36 is rotated between aclosed position at zero degrees (0°) and an open position aligned withthe +90° angle.

Referring to FIG. 8 there is illustrated a side view of the portion ofthe embodiment shown in FIG. 7. The view in FIG. 8 is along the x axiswhen the rotating rod 36 and the magnet 88 are in a fully closed andlatched position. The closed and latched position corresponds to theposition of the magnet 88 in alignment with the point midway betweensensors S2 and S3. The magnet 88 and the sensors S2 (92) and S3 (93) areshown in phantom as being on the opposite side of the rotating rod 36 inthis view. Rotation of the rotating rod 36 is indicated by the arc 138.

Referring to FIG. 9 there is illustrated a graph of signal outputs fromthe array 90 of sensing elements of the magnetic field disturbancesensor shown in FIGS. 6, 7, and 8. The signal outputs S1 (151), S2(152), S3 (153), and S4(154) correspond to the maximum values of signalsprovided respectively by the sensors 91, 92, 93, and 94 as they arescanned at least several times per second. In the illustrative example,the array of sensors 94 may be scanned two to four times per second andyield useable data to detect all relevant events that may occur withrespect to the latch mechanism 32, yet not consume more power from thebattery than is necessary. In the graph, the peak value shown on thevertical axis corresponds to the maximum number of counts of the 10 bitA/D, or 1024 counts representing the strongest amplitude signal from asensor. This value is the peak count value 156. A nominal or medianthreshold 158 (also called a neutral baseline herein) for detection isset during a calibration procedure (to be described for FIG. 17 hereinbelow) at approximately half the number of counts, or 512 counts. Inpractice this actual median value 158 may vary for each sensor S1-S4,and is also influenced by nearby magnetic fields, the noise present,temperature effects, etc. The calibration procedure further allows fordrift in the parameters of the latch monitor 34 in setting the level ofthe actual thresholds 160, 162 for each sensor in the array 90. Thehorizontal axis of the graph of FIG. 9 represents the angulardisplacement of the magnet 88 and the rotating rod 36 through an angleof 180°. This angle may be visualized as approximately + or −90° eitherside of the axis of alignment of the magnet 88 when the container door22 is closed and the rotating rod 36 is latched. This alignment alsocorresponds to the respective sensor output signals 152, 153 fromsensors S2 and S3 that are substantially equal and both above the medianthreshold value 158. This condition is indicated by the dashed line thatintercepts the vertical axis of the graph at 512 counts.

Also illustrated along and below the horizontal axis of FIG. 9 are theapproximate positions of one example of a set of detection zones 164defined as segments of the angular displacement of the magnet 88corresponding to the magnet positions ranging from a fully open doorlatch mechanism 32 and a fully closed and latched door mechanism 32. Thedetection zones 164 are defined for positions of the magnet 88 rotatingin either direction—i.e., from either left or right side—toward theclosed or latched position 166 aligned with the center of the sensorarray 90, depending on which side of the rotating rod 36 the latchmonitor 34 is installed. It will be noted in this example that thedetection zones 164 are not uniform. There are two reasons for this. Onereason is that the angular positions of the magnet 88 that give rise toresponses in the sensors 91-94 are not evenly distributed or spaced whenprojected from the centerline of the rotating rod 36 onto the plane ofthe array of sensors 90, which are evenly spaced from one another.Another reason is because of the way in which the spacing of the sensorsignals S1-S4 is related to the conditions or closure and opening of thelatch mechanism 32 that the array of sensors 90 is configured toresolve. The relative width of the detection zones 164 diminishes as therotating rod 36 approaches and enters angular displacements where theoutputs of the one or two sensors providing a reading near the thresholdlevel (number of counts) is low and approaching the actual threshold 160or 162. This condition is useful when the magnet 88 is producing aresponse in sensors 92 and 93 near a fully latched condition at theposition 166 because that is where the resolution of the sensor array 90needs to be at its maximum.

There are twelve (12) detection zones 164 defined in the illustratedembodiment shown in FIG. 9, identified with reference numerals 0, 1, 2,through 9, 10, and 0. The zero (0) numerals correspond to sensorreadings indicating a fully open door, in either direction, that is, ator beyond the intersection of the sensor characteristics 151, 154 andthe threshold 160, or alternatively, the threshold 162. Thus, there are,in effect, two mirror image sets of zone definitions. One set rangesfrom zone zero at the line 169 in FIG. 9 (door 52 open), through 1, 2,3, 4, and 5 to midway between zones 5 and 6 (door 52 closed and latched,at 0°). The other set ranges from zone zero at the line 170 in FIG. 9(door 52 open), through 10, 9, 8, 7, and 6 to midway between zones 5 and6 (door 52 closed and latched, at 0°). The zone zero is defined in twoplaces in this example, one near −90° at line 167 and the other near+90° at line 168, which correspond respectively to an open door for thetwo possible thresholds 160 and 162. The two sets enable use of thelatch monitor 34 on either side of the rotating rod 36, or for use oneither of the two doors 52 of a typical shipping container 22, foreither clockwise or counter clockwise (CW or CCW respectively whenlooking downward along the rotating rod axis). When the low-numbered setis in use, detection zone 164 numbers 0 (on the right in the figure)through 7 are valid; when the higher numbered set is in use, zone 164numbers 4 through 0 (on the left in the figure) are valid. In any case,a fully closed and latched door 52 lands the magnet 88 substantiallybetween sensors S2 and S3 (and between detection zone 164 numbers 5 and6). In other embodiments, the 1/0 and 10/0 boundaries 169, 170 may bedefined at angles substantially less than 90 degrees.

Continuing with the description of FIG. 9, the signal outputs 151-154for the sensors 91-94 shown approach the maximum or peak values 156 ofthe sensor outputs at the instant the field of the magnet 88 is nearesta particular sensor. If, for example, the magnet 88 is aligned with(i.e., nearest) sensor S3, its output signal will be at or near its peakvalue 156 and the sensor output signals S1, S2, and S4 of the othersensors will be lower in amplitude and either increasing or decreasingdepending whether the magnet 88 is approaching or withdrawing fromproximity to a particular sensor. The detection scheme notes whether therespective signals from the sensors S1-S4 are above or below thethresholds 160, 162 (the calibrated thresholds 160, 162 are representedby the dashed horizontal lines intercepting the vertical axis above andbelow the median count value 158 at 512 counts), and which one of thesignals from two adjacent sensors is the stronger of the two, accordingto the following detection zone definitions, all expressed with respectto the calibrated threshold 160 for the positive-going signals in thisexample:

Zone 0: all sensors below the calibrated threshold 160 (beyond line 169on FIG. 9).

Zone 1: S1 is the only sensor above the threshold.

Zone 2: S1 and S2 are above the threshold, S1 is stronger than S2.

Zone 3: S1 and S2 are above the threshold, S2 is stronger than S1.

Zone 4: S2 is the only sensor above the threshold.

Zone 5: S2 and S3 are above the threshold, S2 is stronger than S3.

Zone 6: S2 and S3 are above the threshold, S3 is stronger than S2.

Zone 7: S3 is the only sensor above the threshold.

Zone 8: S3 and S4 are above the threshold, S3 is stronger than S4.

Zone 9: S3 and S4 are above the threshold, S4 is stronger than S3.

Zone 10: S4 is the only sensor above the threshold.

Zone 0: all sensors below the calibrated threshold 160 (beyond line 170on FIG. 9).

The level of the threshold 160 or 162 is set during a calibrationprocedure (See FIG. 17) to adapt a particular sample of the latchmonitor 34 to a particular container 22. In this example, the threshold160 will be substantially above the median 512 counts—the neutralbaseline 158—as follows. Before describing the calibration procedurehowever, several features and initial conditions need to be mentioned.First, the detection scheme is configured to respond to both positiveand negative swings of the sensor output signals 151-154 relative to themedian or neutral baseline 158 set at half the available number ofcounts (i.e., 512) of the 10 bit A/D. Positive sensor signals—thosehaving excursions between 512 (neutral baseline 158) and 1024 counts156—correspond to the proximity of the south pole of the magnet 88 tothe sensor array 90. Conversely, negative sensor signals—those havingexcursions between 512 (neutral baseline 158) and zero counts—correspondto the proximity of the north pole of the magnet 88 to the sensor array90.

Second, an increasing signal corresponds to a count value moving awayfrom the median or neutral baseline 158; while a decreasing count valuecorresponds to a count value moving toward the median or neutralbaseline value 158. Third, the median or neutral baseline 158 will beexpanded during the calibration procedure to a threshold “window” toaccount for noise and externally influenced drift such as the effects oftemperature variations during transit, nearby magnetic fields that varyfrom location to location, etc. The threshold window thus will bedefined by a maximum number 160 and a minimum number 162 of counts,corresponding respectively to a maximum threshold 160 and a minimumthreshold 162. Accordingly, the thresholds 160 for installations inwhich the south pole of the magnet 88 is proximate to the sensor array90 is set to the maximum number of counts because the sensor signalswill be positive excursions of the count values. Similarly, thethresholds 162 for installations in which the north pole of the magnet88 is proximate to the sensor array 90 is set to the minimum number ofcounts because the sensor signals will be negative excursions of thecount values.

In one example of setting the thresholds 160, 162, one may begin withobtaining a figure for the noise and drift values. Among a number oftested units, the noise range was measured to be in the range of 16 to32 counts. Externally influenced drift in one measurement session was 16counts. Thus, if the drift=−16 counts and the noise=18 counts, athreshold window based only on these factors is the range between 496(512−16) counts and 530 (512+18) counts, respectively the minimumthreshold 162 and the maximum threshold 160. However, these are “openlatch” (corresponding to an open door) values that do not take intoaccount the effects of the actual installation and operation of thelatch monitor 34 next to the rotating rod 36 with the magnet 88.Accounting for these effects is accomplished during an automaticcalibration process (See Task 5, described herein below with FIGS. 10and 17) performed upon installation of a new or replacement unit,replacement of a battery, following a tampering incident, severemagnetic field encounter, etc., all of which are examples of situationswhen the latch monitor 34 may be in an inactive or OFF state.

The calibration process (Refer to FIG. 17), which is Task 5 of thesoftware architecture block diagram illustrated in flow chart form inFIG. 17, may be used to accomplish three functions. First, it sets themedian or neutral baseline values 158 for an open latch mechanism 32.Second, it determines the count values for the rotating rod 36 of thelatch mechanism 32 moving through its range of motion from closed toopen. Third, it calculates the “window” defined by the thresholds 160,162. Task 5 may be performed when the latch monitor 34, followinginstallation on a container door 52, wakes up for the first time. Thecalibration process is performed with the latch monitor 34 installed onthe container door 52 next to the rotating rod 36 selected for theinstallation. When Task 5 is called, typically by a call from the basestation or a signal by the installing technician directly to the latchmonitor 34, the process begins at step 390 by advancing to step 392 totrigger the LEDs 120-126 to blink in a sequence from right to left torequest that the door 52 be opened—i.e., to instinct the installer ortechnician to open the door 52 by operating the latch mechanism 32.Advancing to step 394, the CPU 100 causes the latch monitor circuit 128to read the outputs 151-154 of all of the sensors 120 times whilecapturing (reading), averaging, and storing the maximum and minimumcount values. At step 396, the LEDs are again triggered, to blink in asequence from left to right to request the technician to close and openthe door 52 several times. In step 398 the technician then operates thedoor 52 and the door latch mechanism 32 through complete cycles ofmovement including latching the door 52 in its fully closed conditionwhile the CPU 100 causes the latch monitor 34 to read all of the sensorsS1-S4 to capture (read), average, and store the maximum and minimumcount values.

Proceeding to step 400, the CPU 100 retrieves the values stored in step394 to determine the difference value between the stored maximum andminimum count values for each sensor S1(91)-S4(94). In step 402, if thedifference value is less than 16 counts, the number of counts is set to16. Next, in step 404 the difference value (i.e., a number ≧16) isdoubled and added to the maximum stored value to define the upper(maximum) threshold 160. Similarly, in step 406, the difference value(i.e., a number ≧16) is doubled and subtracted from the minimum storedvalue to define the lower (minimum) threshold 162. The process ofcalibration ends and exits at step 408.

It will be appreciated that the calibration process, besides takingaccount of all of the possible positions of the door latch mechanism 32and the individual sensitivities of the sensors S1-S4, sets thethresholds 160, 162, and the “threshold window” between them at aminimum nominal range of five (5) times the width of the noise windowof, in this example, 16 counts. The value of the multiplier (five inthis example) may be user programmable. Thus, the latch monitor 34sensors S1-S4 should only “see” count values outside the “thresholdwindow” when the magnet 88 in the rotating rod 36 is near a particularsensor. It is important to note that the above description is one ofmany possible particular examples, and is presented to illustrate theprinciples of operation in calibrating the sensors of the latch monitor34 of the present invention.

A further use of the maximum and minimum average values determined instep 398 for each sensor S1-S4 (120-126) with the door 52 closed andlatched is as a signature or fingerprint for the latched door 52 for thecombination of the container 22 and the latch mechanism 32 including thelatch monitor 34. The maximum value set of sensor readings is used whenthe south pole of the magnet 88 is nearest the array of sensors 90. Theminimum value set of sensor readings is used when the north pole of themagnet 88 is nearest the array of sensors 90. The signature of a closedand latched door 52 (i.e., a closed and latched door latch mechanism 32)is essential in determining whether an event involving movement of apart of the latch mechanism 32 is authorized or is incidental or islikely a tampering attempt.

The difference between the thresholds (obtained as described) and thesignature is as follows. The threshold levels 160, 162 established insteps 394 and 396 by the calibration procedure define a reference line166 for determining the location of the magnet 88 in the x-z plane as itrotates when the rotating rod 36 of the latch mechanism 32 is rotated tolatch or unlatch the door 52 of the container 22. The algorithm comparesthe relative amplitudes of the sensor signal outputs 151-154 withrespect to the corresponding threshold 160, 162 and to each other todetermine the location of the magnet 88—i.e., the angular position inthe x-z plane of the magnet 88. The signature is a single set ofindividual sensor values 151-154 determined during step 388 for a closedand latched door 52 of a particular container/latch monitor combination.The single set of sensor values 151 to 154—four data points—is unique tothat door/latch monitor combination, and thus very useful in determiningwhether a container breach or attempted breach has occurred.

It will be appreciated that the novel combination of the magneticsensing design and the analysis and interpretive processing of thesignal outputs of the array of sensors 90 enables a substantial abilityto detect and report a wide range of conditions of the latch mechanism32 of a shipping container door 52. These conditions include authorizedoperations of the latch mechanism 32 and unauthorized incidents(tampering) as well as incidental events that may occur during storage,loading and unloading, and transit. The sensor system in the latchmonitor 34 is configured to detect and report a range of authorizedoperations that correspond to a closed and latched door, a closed butunlatched door, a partially open door, and a fully open door. It is alsoconfigured to detect movement of the latch components due to bufferingby the wind and to vibration and bump shock such as encountered duringtransit of the container 22 or handling of the container in a containeryard 60, etc. Further, the sensor system detects movement of thecomponents of the latch mechanism 32 that can only occur during effortsto break the closed and latched condition by application of externalforce or attempts to open the latch mechanism at times when thecontainer 22 is not scheduled for unloading, inspection, or loading.Moreover, the sensor system is capable of detecting efforts to disarm orimpair the sensing ability of the sensing mechanism by using externalmagnetic fields or shielding in proximity to the latch monitor 34. Evenelectromagnetic events occurring during thunderstorms may be detectedand result in a logged detection event. The logged events can beretrieved and reported to a base station 42 or yard server 12, or from ahandheld terminal 28 within or outside a container yard 60 by authorizedinspection personnel such as government customs officers or othersecurity or transportation officials.

Even though the array of sensors 90 are disposed in a row parallel tothe z axis, it is still possible to distinguish movements of the magnet88 in the x or y directions. Assuming the door 52 of the container 22 isclosed and latched, movement of the magnet 88 in the x direction (i.e.,toward or away from the door 52), without changing the sensor outputs inthe z direction, will affect all of the sensor output levels 151-154(See FIG. 9) by a proportional amount, that is, they will all increaseor decrease together in proportion to the displacement of the magnet'sposition. This is in contrast to the movement of the magnet 88 in thex-z plane about they axis, where the outputs 151-154 of the sensors inthe x direction will vary as the magnet 88 moves in the z direction.This example illustrates a circumstance in which an attempt is made topry the rotating rod away from the latch monitor 34 or vice versa.

Similarly, again assuming the door 52 of the container 22 is closed andlatched, movement of the magnet 88 in they direction will again affectall of the sensor output signals 151-154 in the same way, in contrast tomovement of the magnet 88 in the x-z plane, where the outputs 151-154 ofthe sensors will have essentially no change in they direction; in fact,they axis sensor outputs 151-154 will nominally be zero through out therange of motion of the rotating rod 36 if the latch monitor 34 has beenproperly installed. This example illustrates a circumstance in which anattempt is made to move the rotating rod 36 up or down, or more likely,it may just indicate normal vibration or jarring of the rotating rod 36during transport of the container 22.

In another example, the sensor array 90 can easily determine whether anexternal magnet is being manipulated close to the latch monitor in anattempt to tamper with it. To illustrate, suppose the magnet 88 is aimedat sensor S3 (124) and the latch monitor 34 detects an increasedamplitude of the output of sensor S1 (120) while noting also that sensorS2 (122) is still in the neutral state (i.e., its output is below thethreshold). This is an indication of the presence of the external magnetclose to sensor S1 (120) because both S1 (120) and S3 (124) areindicating high amplitudes, which cannot happen at the same time withoutstimulating sensor S2 (122) at the same time.

These results accrue because the field strengths and the correspondingsensor signal count values 151-154 are all relative. The system isconfigured to regard sensor output signals 151-154 that change in thesame direction together as indicating an unauthorized event ortampering. This principle is similar to the concept of common moderejection of noise along balanced transmission lines. Thus, motion ofthe magnet in the x or y directions causes the signal strength of allfour sensors to increase or decrease together, while the latch monitor34 tracks motion of the magnet in the z direction.

Some specific examples of motion of the rotating rod 36 (except rotationof the rotating rod) that will trigger an event accompanied by an alertinclude the following. (1) If the rod moves laterally more thanapproximately 0.250 inch away from the latch monitor 34, a door openevent will be indicated. (2) If the rod 36 moves laterally more thanapproximately 0.050 inch towards the latch monitor 34, a magnetictampering event will be indicated. (3) If the rod 36 slides verticallymore than approximately 0.250 inch either up or down, a door open eventwill be indicated. (4) If a foreign magnet is placed such that itinterferes with the relative signal strengths of the sensor outputsignals 151, 152, 153, and 154 (i.e., the respective count values), amagnetic tampering event will be indicated. (5) If a foreign magnet isplaced such that it causes a sensor 91, 92, 93, or 94 of the latchmonitor 34 to “leave” its calibrated minimum/maximum window, a magnetictampering event will be indicated. Leaving its calibrated min/max windowmeans that the count value produced by the sensor is out of range of thecalibrated min/max window and/or the count range of the input of the A/Dconverter 102 in the CPU 100 of the latch monitor circuit 120 shown inFIG. 5. In conjunction with the motion sensor 116 (the “At Rest”sensor), an event will occur and an alert will be issued when thecontainer 22 begins to move and following a predetermined settling timehas expired after motion of the container 22 has ceased. Thepredetermined settling time may be set at approximately one minute, forexample. Alerts are discussed in the description for FIG. 10 at step212.

From the foregoing it is to be understood that the sensor array 90 andthe associated circuits 128 in the latch monitor 34 can detect a widerange of movement of the rotating rod 36 in all three axes andaccurately distinguish both tampering events and incidental events fromauthorized operation of the latch mechanism 32 of the container 22. Thisis accomplished by interpreting signal values produced by the sensors91-94 that exceed preset limits or which do not match a predeterminedprofile established during a calibration process. The latch monitor 34is also able to detect attempts of tampering that do not involvemovement of the rotating rod but do involve attempts to trick the sensorarray using an external magnetic field. Further, the latch monitor canas easily detect naturally occurring events such as lightning strikesduring a thunderstorm in the vicinity of the container 22. Such attemptsor natural events, which distort the profile established for a closedand latched magnet 88, will be logged in memory, and cause an alertsequence to be initiated if preset limits are exceeded. The same is trueof attempts to insert a magnetic shield between the magnet 88 and thesensor array 90. All data monitored by the latch monitor may be loggedfor later analysis and review by authorities.

Referring to FIG. 10, there is illustrated one embodiment of a softwarearchitecture presented as a flow diagram for use in the latch monitor 34of the present invention. The software is needed to manage the variousprocesses that take place in the latch monitor 34. Software modules areincluded for the Tasks 1 through 5 and for other functions such as poweron self test (POST), event logging, alert sequence, etc. In general,each task in the system records its own events using an event loggerservice. A master task, Task 0 (zero), monitors these events as theyaccumulate in an event logger 208 and then directs the communications,GPS, sensor monitor, and power management tasks (Tasks 1, 2, 3, and 4)as appropriate. When an alert condition is detected, the latch monitor34 through Task 0 will attempt to communicate with the base station 42to transfer its log contents. Once such transfer is completed, the latchmonitor 34 will attempt to locate its current position via the GPS Task2, then again attempt to transfer the log contents to the base station42. As will be described herein below for Task 4, each task isresponsible for controlling the ON-OFF state of the section of the latchmonitor circuit 128 that it controls with the common goal of powerconservation. Optimal control of each circuit section has beendetermined based on operational testing.

The flow chart shown in FIG. 10 illustrates one way in which thefunctions of these modules may be organized. The flow begins with theStart block 200 and advances to step (or module) 202 to execute a POSTand initialization routine. The POST and initialization step isresponsible for testing all functional components in the latch monitor34. It reports errors as appropriate on the LED indicators. Afterinitializing all of the circuit sections and calibration of the array ofsensors 90, control is passed to Task 0 (zero) to manage the systemoperations.

Step 202 is followed by a test step 204, via a query and reply with theevent logger 208, to determine whether calibration of the sensors hasbeen completed. If the reply from the event logger 208 is negative,indicated by a letter N, then the flow proceeds to Task 5, calibration,at step 206 to perform the calibration process, then return a completionindicator (e.g., a flag bit) to the event logger 208. If a Task 5completed bit is present, then the flow returns along the pathdesignated Y (for YES) to step 208, the event logger, and continues tostep 210 to check for an alert event indicator or alert data logged inmemory. If an alert has been logged, the flow advances to step 212 toinitiate and complete an alert sequence. If no new alert has beenlogged, the flow skips the alert sequence and enters step 214, which isTask 0 (zero). Task zero at step 214 acts as a task manager to monitorthe alert sequences and to launch and control other tasks in turn withthe aid of step 216, a counter, before advancing to each Task 1 through4 as required.

The other functional Tasks 1 through 4 include Task 1 at step 218,“Communications,” which is responsible for providing input and output ofpacket data signals over the ZigBee® radio interface, via transceiver106 (See FIG. 11). Task 2 at step 220, “GPS Processing,” (FIG. 12)controls the GPS interface to determine the location of the latchmonitor 34 and writes data to the event logger 208 as requested and atpredetermined intervals. Two types of location reports are logged,immediate location and refined location. Immediate location data from aninitial reading is taken without regard for precise accuracy. Refinedlocation data is provided after several readings based on known GPSparameters to allow iteration toward a reading of less uncertainty.

Task 3 at step 222, “Sensor Monitor,” (FIG. 13) monitors and logs theoutput signals S1-S4 of the HES sensors 91-94 respectively. As one ofthe power saving features of the latch monitor 34, the HES sensors91-94, may be turned ON and OFF (See, e.g., FIG. 13) and/or powered byI/O pins of the CPU 100. Task 3 may also monitor and log the “At Rest”sensor 116 (alternatively, motion sensor 116). The “At Rest” sensor 116is read by an interrupt service routine, and a timer may be reset everytime motion is detected. The sensor monitor task 3 would then check thetimer and track the present state of the container 22. The data from themotion sensor 116 may be used by other tasks to control their respectiveoperation. For example, the GPS Task 2 may be inhibited from takingreadings as long as the latch monitor 34 (and container 22) are stopped,i.e., not in motion, to reduce power drain on the battery. However,readings of the location may still be taken at long intervals, e.g.,hourly, to provide a sufficient record. In another example, the sensormonitor Task 3 may use the data from the motion sensor 116 to reduce thesensitivity of the HES sensors 91-94 if needed such as when thecontainer 22 is in motion during transport and there is less need fordetecting small displacements of the latch mechanism 32. The data fromthe sensors 91-94 and the “At Rest” sensor 116 is written to the eventlogger 208. Examples of events that may be logged during Task 3 include“Motion Started,” Motion Stopped,” “Door Open,” and “Door Closed.” Otherevents may include “Normal Vibration” and abnormal indicators forerratic signals along the x, y, or z axes that may indicate tamperingattempts.

Task 4 at step 224, “Power Management,” (FIG. 15) controls and monitorsthe usage of power by the latch monitor circuits 128, including writingdata to the event logger 208 about the battery power level and the mainsupply voltage to the circuits, Vcc, in the event of a change in eitherparameter. Task 4 may also generate an hourly “power status” reportkeyed by the real time clock 112, for the purpose of tracking batterylife.

Task 5 at step 206, “Calibration,” (FIG. 17) performs calibration of thearray of sensors 90 in the latch monitor 34. As described herein above,it is the first task performed following the POST and initialization ofthe latch monitor circuits 128.

FIG. 11 illustrates a flow chart diagram of a communications Task 1process for use in the embodiment of FIGS. 4, 5, and 10. The processstarts at step 230 to initialize the transceiver 106 in the latchmonitor circuit 128. In this function, initialization in step 230 resetsring buffers for incoming commands and data, purges a receive queue,then sleeps for a preset time (five seconds in this example) to allowother processes to be completed. Step 230 is followed by step 232 towake up the uART and modem on process check in. If this step issuccessful, as tested in step 234, the flow proceeds to step 236 todetermine whether there are data logs to send? If YES, the processadvances to step 238 to send the log file and clear the log flags upon asuccessful transmission. Step 238 is then followed by a step 240 torequest a disconnect. Returning to step 234, if the test was notsuccessful, the flow advances directly to the step 240 to request adisconnect. Similarly, in step 236 if there are no data logs to send,then the process steps directly to the step 240 to request a disconnect.In step 242 a test is made to determine if the request to disconnect wasgranted and if the response is NO, the flow proceeds to step 248 toprocess additional commands queued up from the host (Task 0, the “TaskMaster”), then returns to the input of the step 240 to re-enter theprocess at the step 240, the request to disconnect. If the disconnectrequest was granted, however, the process advances to step 244 to turnoff the uART and the modem, and then go to sleep in step 246 until thenext “check in time.” The check in time may be controlled by aprogrammable timer within step 246, followed by a return to step 232 towake up the uART and modem once again.

In the flowchart of FIG. 11, the step 248 to “Process additionalcommands from host” may include a number of functional operations suchas receiving and storing a manifest or update thereto, or accessing andtransmitting the stored manifest, uploading alert data or other loggeddata, re-determining the location data, performing a new calibration(Task 5) or processing other T asks, etc. One of the novel features ofthe latch monitor 34 of the present invention is its ability to storemanifests in memory 104 within the CPU 100. Thus every container havinga latch monitor 34 in the system can have the contents of the container22 stored at the container, readily available for access simply onsending a command to the latch monitor 34. The data may be returned viathe transceiver 106 by merely initiating an “update manifest” routine inthe latch monitor circuit 128. As described herein above, such updateroutines are well-known in the art and will not be further describedherein. One advantage of having the manifest stored at the container isthat, in the event of an incident involving unauthorized movement ortampering with the container or its involvement in an accident, thecontents can be completely and accurately known on site and in real timeto promptly enable the most appropriate response to the incident.

Referring to FIG. 12 there is illustrated a flow chart diagram of a GPSTask 2 process for use in the embodiment of FIGS. 4, 5, and 10. Theprocess begins with an initialization step 250, to set up defaultpositions to report in the absence of readings, then turn on a pull upresistor to activate power control for the GPS circuit. The circuit thensleeps for a preset time interval (ten seconds in this example) to allowthe completion of other processes, followed by defining the first GPSreading as an attempt to obtain a refined GPS reading. Step 250 isfollowed by activating the GPS receiver 114 and waiting for a lockindication in step 252. Upon receiving the lock indication, a log entryfor GPS activity is made in step 254 before advancing to step 256 toverify whether lock was obtained. If NO, the flow proceeds to step 258to log an entry for failure to lock, followed by setting a defaultlocation as the latest reading in step 260 and placing that reading in aglobal variables register in step 262. Then the flow advances to step264 to turn OFF the GPS receiver 114 and end the task—i.e., the taskenters sleep mode in step 266 until the next reading, returning to step252 to await a lock indication.

Returning to step 256, if a lock indication was obtained, the processflows to step 268 to log the entry for the initial reading and then testthe reading in step 270 to verify whether the location reading was aso-called “quick reading,” that is, a lock obtained upon a firstsuccessful reading of the data necessary to establish a signal lockcondition, indicating that the location estimation to refine the readingmay begin. As is well known, the GPS receiver measures the time anavigation message is received from each of several satellites andsolves for the rectangular coordinates and the time of its own locationand estimates the distance between the satellite and the GPS receiver.Generally, information from four satellites enable the GPS receiver todetermine a first approximation of its location. Refinement of thelocation may be determined through iteration.

Continuing with FIG. 12, if the result of the query in step 270 is YES,the process flows to step 262 to place the latest reading in a globalvariables register, followed by turning OFF the GPS receiver 114 in step264 and ending the task—i.e., the task enters sleep mode in step 266until the next reading, returning to step 252 to await a lockindication. Returning to step 270, if the result of the test is NO, theflow advances to step 272 in which the GPS receiver 114 waits for 16consecutive readings that are within a predetermined tolerance, thenperforms a test step 274 to determine if the required number ofin-tolerance readings was received. If NO, the task branches again tosteps 262 to 266 to store the latest reading in global variables, turnoff the GPS receiver, and go to sleep until the next reading. If,however, 16 in-tolerance readings were received the flow advances fromstep 274 to step 276 to log the entry for a refined reading beforeproceeding to step 262 to store the reading, etc. as explained hereinabove. It will be appreciated by persons skilled in the art that loggingGPS location data along with time and event data such as the status ofthe container door, the status of the container itself—for example,whether it is in storage or transit, at rest or in motion, whether it isinvolved in a breach attempt, etc.—can be invaluable in responding toincidents that place the container and its contents at risk of loss ordamage.

Referring to FIG. 13 there is illustrated a simplified flow chartdiagram of a sensor Task 3 process for use in the embodiment of FIGS. 4through 10. The flow begins with step 280 to perform the followingfunctions: initialize a “DoorState” holder, define a starting sensor forscanning the array of sensors 90, setting an initial zone to zero (0)(i.e., for an open door), and initialize the variables for the minimumand maximum sensor readings. Following initialization of the processor100 in step 280, the sensors of the sensor array 90 and the motion (AtRest) sensor 116 are turned ON or enabled in step 282 and read in step283 to obtain data for the position of the magnet 88 in the rotating rod36 and to detect motion of the shipping container 22. In step 284, ifYES, the position of the magnet 88 has changed, the flow advances tostep 286 to log the new position of the magnet 88 and determine whetherthe container door 52 is open, closed, or has been moved. In step 288,if the condition of the container door 52 is not authorized, i.e., itdoes not correlate with an actual opening or closing of the containerdoor, the logged event data is interpreted and an alert sequence isinitiated and the flow advances to step 290.

Continuing with FIG. 13, in step 290 the process turns its attention toa background task that began if the motion sensor 116 outputted a pulseafter the sensors were enabled in step 282. Such an output pulse occurswhen any motion of the container is detected. The process in step 290begins to count the number of output pulses of the motion sensor 116that occur within a user-setable period of time, e.g., “ΔT” seconds. Inthe illustrative embodiment, setting ΔT=60 seconds has been shown to bea suitable length. In the following step 292, the number of pulses iscompared with a limit value “P,” which may be set by the user to somevalue, say ten (10) pulses. Thus, if the number of pulses counted withinΔT exceeds the limit value P, the process advances from step 292 to step294 to log the new resting/moving status. Thereafter, an alert sequencemay be initiated in step 296 and the flow proceeds to step 297. In step297, the sensors are turned OFF or disabled. In the following step 298 asleep timer begins a brief sleep interval before the process returns tostep 280 to read the sensor array 90 and the motion sensor 116 of FIG.5. Returning to step 292, if the number of output pulses from the motionsensor 116 does not exceed the limit value P within the time ΔT, theflow follows the “N” path directly to step 297, where the process endsand is re-initiated at step 280 following a brief sleep cycle. It willbe noted by persons skilled in the art that steps 282 and 297,respectively sensors ON and sensors OFF, are separately performed toenable control of the power consumption in the latch monitor 34. In someembodiments these steps may be deleted if, for example, conservation ofpower is not critical.

It will be recalled from the detailed description about FIGS. 4 through9 that the array of sensors 90 in the latch monitor 34 is configured todetermine the position of the magnet 88 that is installed in therotating rod 36, using the measured data about the magnet position tointerpret this data and determine the condition of the latch mechanism32 of the container 22. The purpose of the 29 latch monitor 34 is todetect a breach of the container and the conditions of the container atthe time of the incident, store the data, and communicate the data (asin an alert sequence or other message) on command from abase station ora container yard server or other authorized terminal (See FIGS. 1 and2). The arrangement of the sensors 91-94 enables the latch monitorcircuits 128 to track the status of the latch mechanism 32 and interpreton a continuing basis what the measurements of the magnet position meanas to the kind of event experienced by the container door 52. Theprocessing undertaken in the latch monitor 34 to accomplish thesefunctions takes place primarily during the steps 284 (magnet positionchanged?) and step 292 (Number of pulses exceed P?, corresponding to thequery “has the rest/motion state changed?”). These functions areaccomplished through the execution of the routines described. There issufficient information presented in the description of FIGS. 5 through 9and in the flow chart diagrams presented herein to enable personsskilled in the art to construct a suitable data acquisition, analysis,and interpretive program to perform these functions.

Referring to FIG. 14 there is illustrated a block diagram of a powersystem for use in the embodiment of FIGS. 4, 5, and 10. It will be notedthat, for reasons of clarity, the return path for current in eachfunctional block of the system, though not shown in the figure, isassumed to be present. The power system 300 derives operating currentfrom a battery 302 that delivers nominally 3.6 Volts to the input of ahigh efficiency power supply 304. The battery 302 may preferably be asingle Lithium Ton (Li I) cell. Power supply 304 may preferably be aswitchmode regulator that operates at very low currents as it provides aregulated 3.3 Volts at its output. The operation of the power supply 304itself may be enabled by a control signal from the power monitorfunction 308. A capacitor 306 (a “supercap”) of 2.5 to 10.0 Farads isconnected across the output of the power supply 304. Thus, the capacitor306 supplies operating current to the circuit loads or the latch monitorcircuit 128 during the brief time each is operational, while the powersupply 304 maintains a sufficient charge on the capacitor 306. The loadsconnected to a terminal of the capacitor 306 of the power supply 304 areeach separately controlled through a series FET switch to supply poweron demand as determined by a power control function 310. The powermonitor 308 (including anticipation logic) and power control 310 may beimplemented as firmware functions resident in the CPU 100.

The power monitor 308 operates to log various present voltage levels (asin step 360) at user-settable timed intervals as follows. The voltagelevels may each be defined as a “battery state N,” where N=0 through 7,for example. Thus, an alert leading to an alarm may be initiated bycertain ones of the “Batt States” during the step 356 process powerstates in sequence. For any power state (or “Batt State”) that haschanged, it becomes e.g., a “New State,” and an alert may be issued forprocessing by the CPU 100. In the illustrated embodiment, the “BattStates” may be defined as follows:

Batt State 1 indicates that a first user set alarm level has beenreached;

Batt State 2 indicates that a second user set alarm level has beenreached;

Batt State 3 indicates when the battery voltage is below critical (Vbatt<3000 mVolts);

Batt State 4 indicates when the Vcc voltage is below critical (Vcc <2900mVolts); and

Batt State 7 indicates when Vbatt <2000 mVolts.

Batt State 0 may indicate some functional statement, e.g., “Here are thevoltage readings . . . ” Batt states 5 and 6 may be reserved. Further,the power states, as in this example, may be recorded and/or reportedeach hour per step 364.

Continuing with FIG. 14, the radio 312 (task 1), connected to the Vccbus 348 at the output terminal of the capacitor 306 through a FET 322,receives control signals from the power control circuit 310 on gate lead332. Similarly, GPS 314 (task 2) is controlled by FET 324 on gate lead334, data flash 316 is controlled by FET 326 on gate lead 336, pressuresensor 318 is controlled by FET 328, calibration 320 (task 5) by FET330, and sensors 342 (task 3) by FET 342. In operation, each FET switchis controlled according to which particular circuit is needed to beactive at each step in each task. The logic includes recognition whenone circuit in use requires another circuit's function to be completedbefore disconnection. An example is keeping the communication taskcircuit (transceiver 106) in the latch monitor circuit 128 operatinguntil the requirement for data from the data flash function iscompleted. Each of the tasks in the control system is responsible forturning OFF its connection to the power supply when it is not in use.This use of one power supply for a plurality of individually switchableloads controlled by the on-demand needs of the individual branches ofthe circuit enables the battery 302 to operate for months withoutreplacement or recharging.

Referring to FIG. 15 there is illustrated a flow chart diagram of apower monitor Task 4 process for use in the embodiment of FIGS. 4, 5,10, and 14. The purpose of the power task is to track the status of thebattery voltage and the value of the Vcc voltage that supplies thecircuits in the latch monitor circuit 128, and log the power state atregular intervals to track battery life. The power monitor Task 4 beginswith a step 350 to initialize the power monitor task followed by turningon the resistor dividers in the A/D converter section 102 of the CPU 100in step 352. Step 354 follows, wherein the analog value of the supplyvoltage Vcc bus 348 (See FIG. 14) is read and digitized in the A/Dconverter 102, converting the analog voltage into digital numbers orcount values, and logging the event.

Continuing with FIG. 15, step 356 retrieves the measured count value toprocess the power state indicated by the count value for Vcc. The powerstate is tested against the previous value in step 358 and the new statelogged in step 360 if the state has changed. If the power state has notchanged, the log new status step is skipped and the flow advances tostep 366 to turn OFF the resistor dividers in the A/D converter 102 and“go to sleep” until the time for the next reading to be made. From step366, the process pauses at a timer in step 368 before advancing to thebeginning of the power management task into step 352 as described hereinabove. The time value in the exemplary embodiment is shown as one hour,but may be set to another value consistent with the application. In atypical case, the CPU 100, when monitoring the event log and checkingits contents against the corresponding stored reference values, willgenerate an alert when a value is out of tolerance and forward theindiction to process an alert sequence. As described herein above, analert sequence may culminate in a signal to the LEDs or to thecommunications task for transmission to the base station or to the yardserver, for example.

Referring to FIG. 16 there is illustrated a flow chart that summarizes aprocess or method for maximizing battery life in the exemplary latchmonitor 34 of the present invention. Each of the steps in this processare embodied in the latch monitor 34 as described in detail for severalof the figures herein. For example, refer to FIGS. 4, 5, and 10 through15. Considered together, the combination of steps shown in FIG. 16results in considerable savings of power and an extended battery life.This is an important consideration for a device such as the latchmonitor 34 described herein and attached to a shipping container thatmay be in transit or storage for considerable periods of time.

Continuing with FIG. 16, the flow begins at a start step 370 followed bystep 372 to connect the output of the battery 302 to a switchmode, lowcurrent regulator 304 loaded by a supercapacitor 306. Next, in step 374couple each circuit in the system—here the illustrative latch monitor34—that requires current to the output of the supercapacitor 306 via alow-loss switch such as FET switches 322, 324, and 326. Thereafter theflows proceeds to step 376 to control the respective low-loss switch (itdoes not have to be a FET switch; it could be implemented by other typesof semiconductors) at each circuit according to the need for current bythat circuit. The foregoing steps are illustrated in FIG. 14. The flowthen advances to step 378 to cause selected ones of each of the circuitsdrawing power to enter a dormant mode when operating current is notrequired. As an example, refer to a step in each of FIGS. 11-14 thatinclude a “sleep” step near the end of a routine. Step 378 is followedby step 380 to operate signal analysis tasks performed in one or morecircuits independently of signal acquisition tasks, storing the acquiredsignals for subsequent analysis. One example (see FIG. 5) of this step380 occurs in the CPU 100, which stores signal data output from the A/D102 in memory 104 for later analysis as a background task. Performingthe analysis during the signal acquisition uses considerably more powerwhen the CPU 100 is active, than separate operation of these tasks. In afollowing step, 382, the system may monitor battery output voltageand/or power supply output voltage as a prelude to initiating powerconservation or alert sequences, as described for FIG. 15. The methodsfor maximizing battery life concludes, in this example, with an exitstep 384.

Referring to FIG. 17 there is illustrated a flow chart diagram of acalibration Task 5 for calibrating the magnetic disturbance sensor ofthe embodiment of FIGS. 4 through 10. This auto calibration routinebegins at step 390, followed by step 392 to trigger the LEDs 120-126 inthe status indicator 118 to blink in sequence from right-to-left (inthis example). This right-to-left sequence is a signal to an installeror technician to open the container door 52. Opening the container door52 moves the magnet 88 away from the sensors 91-94 so that their outputswill be below the threshold value that is initially set at the medianlevel 512 counts. Next, in step 394 the CPU 100 causes the A/D converter102 to read and measure the sensor output values, average them over apredetermined number of measurement cycles (120 times in this example),and store the resulting maximum and minimum count values for thecondition of a fully open door.

Continuing with FIG. 17, the flow begins at a start step 370 followed bystep 372 to connect the output of the battery 302 to a switchmode, lowcurrent regulator 304 loaded by a supercapacitor 306. Next, in step 374couple each circuit in the system—here the illustrative latch monitor34—that requires current to the output of the supercapacitor 306 via alow-loss switch such as FET switches 322, 324, and 326. Thereafter theflows proceeds to step 376 to control the respective low-loss switch (itdoes not have to be a FET switch; it could be implemented by other typesof semiconductors) at each circuit according to the need for current bythat circuit. The foregoing steps are illustrated in FIG. 14. The flowthen advances to step 378 to cause selected ones of each of the circuitsdrawing power to enter a dormant mode when operating current is notrequired. As an example, refer to a step in each of FIGS. 11-14 thatinclude a “sleep” step near the end of a routine. Step 378 is followedby step 380 to operate signal analysis tasks performed in one or morecircuits independently of signal acquisition tasks, storing the acquiredsignals for subsequent analysis. One example (see FIG. 5) of this step380 occurs in the CPU 100, which stores signal data output from the A/D102 in memory 104 for later analysis as a background task. Performingthe analysis during the signal acquisition uses considerably more powerwhen the CPU 100 is active, than separate operation of these tasks. In afollowing step, 382, the system may monitor battery output voltageand/or power supply output voltage as a prelude to initiating powerconservation or alert sequences, as described for FIG. 15. The methodsfor maximizing battery life concludes, in this example, with an exitstep 384.

The upper and lower limits of the threshold window are determined insteps 404 and 406 respectively. In step 404, the difference value ismultiplied by two and added to the maximum count value stored in step398 for a closed and latched container door 52. In step 406, thedifference value is multiplied by two and subtracted from the minimumcount value for a closed and latched container door 52. Thus, thethreshold window is approximately five times the difference value (i.e.,the noise width) and is centered approximately on a median orintermediate count value of the input range of the A/D converter 102.The value of the multiplier (five in this example) may be userprogrammable. The upper and lower threshold values provide a referenceagainst which sensor outputs corresponding to movements of the magnet 88away from a closed and latched position can be detected and evaluated.Once these limits are established, the auto calibration sequence ends atstep 408 and the routine exits.

The foregoing detailed description is based on the use of a magneticdisturbance detector, comprising a magnet, an array of magnetic sensorsand associated processing circuits, for detecting movement of a movablecomponent of a door latch assembly relative to a fixed or stationarycomponent of the door latch assembly mounted on the container or otherarticle having a need for a mechanical latch. The magnet may be apermanent magnet as described herein or an electromagnet. A magneticdisturbance detector is one example of a disturbance detector thatoperates using an electromagnetic flux field, as described in detailherein above. Another example that is usable for the same purpose andthus represents an alternative embodiment contemplated herein is the useof tight energy as the medium for signaling the relative positions ofthe components of the latch assembly. For example, a light emittingdevice such as a light emitting diode or other light source may be usedin place of the magnet such that the beam of light from the lightemitting device provides the “flux.” Then, an array of light sensitiveelements such as photo diodes, photo cells, photo transistors,charge-coupled devices, image sensors, or the like could be used todetect the beam of light or flux from the light emitting device. Thelight sensing elements occupy the same positions as in the magneticdisturbance detector, and the circuitry and remaining components of thelatch monitor 34 are essentially the same, with adjustments in designbeing made to accommodate the interface with the light devices. In suchan embodiment, the wavelengths of the light energy need not be limitedto the visible spectrum. Similar disturbance detectors operating onelectromagnetic flux, using emitters and sensors not yet commonlyavailable, could of course be used.

In another embodiment, the number of sensors used in the array ofsensors 90 (see FIGS. 4, and 6 through 9) may be varied. While four suchanalog Hall Effect sensors (HES) are used in the illustrated embodiment,it is also possible to provide a system for detecting the condition ofthe door latch using only two sensors, placed in the positions of thesensors S2 and S3 as shown in the FIGS. 4, 6, 7, 8 and 9. Such an arrayprovides somewhat less information about the position of the movableportion of the latch assembly but is nevertheless able to differentiatea closed and latched door from one in which the door latch is not fullylatched or is open, either partially or fully. Moreover, a two-sensorarray, using the same processing circuitry adjusted for operation withtwo sensors instead of four, is still able to detect other conditionsindicating tampering or incidental events. Alternatively, instead ofanalog HES devices, digital HES devices may be used to measure thetiming between the activation of the sensors corresponding to themovement of the rotating rod. Further, with either type of sensor, theoutput of the motion sensor may be combined with the magnetic sensordata to more accurately determine the behavior of the system. Forexample, if it is sensed that the container is moving, and disturbancesin the magnetic field are also detected, it could mean that thecontainer is being moved while still on a trailer.

Persons skilled in the art will also recognize that the door latchdisturbance detector of the present invention may be used with a latchrod that moves longitudinally—i.e., slides along its longitudinalaxis—as well as rotating about its longitudinal axis. In bothembodiments, the detection system is responsive to the translation ofthe flux emitting element within a plane of motion. The flux emittingelement either rotates in a plane back and forth past the array ofsensors disposed in the same plane, or the flux emitting element moveslinearly back and forth (or, up and down) past the array of sensors inthe same plane. It is simply a matter of arranging the sensors in thearray in the required orientation. For example, referring to FIG. 4, 6,or 8, simply rotating the array of sensors 90 by 90 positions the arrayof sensors 90 to detect disturbances to a latch rod 36 that moves alongits longitudinal axis to latch or unlatch it.

While the invention has been described and illustrated in only one ofits forms, and even several alternative embodiments, it is not thuslimited but is susceptible to various changes and modifications withoutdeparting from the spirit thereof.

What is claimed is:
 1. A method for detecting movement of a shippingcontainer latch, comprising the steps of: attaching a magnet to amovable portion of said shipping container latch; installing a sensingunit having a processor and first and second sensing elements coupledthereto on a stationary portion of said container latch and proximate toa path traversed by said magnet for detecting changes in a magneticfield profile caused by movement of said movable portion of saidcontainer latch; and processing data in said sensing unit representingsaid changes in said magnetic field profile to determine whether saidmovement of said container latch is authorized or incidental or atampering incident.
 2. The method of claim 1, further comprising thesteps of: generating a data message containing information derived insaid processing step; and transmitting said data message via acommunication network to an external control terminal.
 3. The method ofclaim 1, wherein said attaching step comprises: installing a straightbar magnet in said movable portion of said latch; wherein an axis ofsaid magnet is aligned substantially perpendicular to movement of saidmovable portion.
 4. The method of claim 3, wherein said installing stepcomprises: orienting one pole of said magnet toward said sensing unit.5. The method of claim 1, wherein said attaching step comprises:installing a straight bar magnet in said movable portion of said latch,wherein said movable portion of said latch is configured as a rotatingmember to rotate about an axis; wherein an axis of said magnet isaligned along a radius of said rotating member.
 6. The method of claim5, wherein said installing step comprises: orienting one pole of saidmagnet toward said sensing unit.
 7. The method of claim 1, wherein saidinstalling step comprises: configuring said sensing unit with at leasttwo sensing elements spaced apart; disposing said at least two sensingelements such that outputs of said sensing elements are responsive tochanges in position of said magnet as said movable portion of saidcontainer latch is moved; coupling a processing circuit to said outputof said sensing elements for converting said outputs to digital form forstorage in a non-transitory memory coupled to said processing circuit;and storing said digital form of said outputs of said sensing elementsin a non-transitory memory segment.
 8. The method of claim 7, whereinsaid configuring step comprises: specifying that said at least twosensing elements are Hall Effect Sensor (HES) devices.
 9. The method ofclaim 7, wherein said configuring step comprises: aligning four HallEffect Sensor (HES) devices in a straight line array within said sensingunit and substantially within a plane of movement of said magnet; anddisposing said array perpendicular to a longitudinal axis of said magnetwhen said moving portion of said container latch is locked in a closedand latched condition.
 10. The method of claim 1, wherein saidprocessing step comprises: comparing said data representing said changesin said magnetic field profile with a stored signature profilecorresponding to sensor data representing a closed and latched containerdoor; and confirming a closed and latched condition of said containerdoor if no disparity relative to said signature profile is found; oranalyzing said data representing said changes in said magnetic fieldprofile if a disparity relative to said signature profile is found. 11.The method of claim 10, wherein the step of analyzing comprises:determining whether said disparity relative to said signature profile isan indication of an incidental event or a tampering event; logging analert if said disparity indicates a tampering event; and initiating analert sequence if said indication is determined to be a tampering event.12. The method of claim 2, wherein said generating step comprises:retrieving data from a non-transitory memory segment corresponding tomeasurements of said sensing unit of said changes in said magnetic fieldprofile; formatting said data in a data message; and configuring saiddata message for coupling to a transmitter.
 13. The method of claim 2,wherein said transmitting step comprises: coupling a signal containingdata representing said changes in said magnetic field profile to atransmitter input; and transmitting said signal to said externalterminal through said communication network.
 14. A sensing apparatus fordetecting movement of a shipping container latch, comprising: a magnetdisposed within the body of a movable portion of the shipping containerlatch; a housing attached to the shipping container proximate saidmovable portion of said container latch; a plurality of magnetic fieldsensors disposed in a uniform, predetermined configuration and supportedby said housing proximate said magnet, each said sensor providing anoutput signal proportional to a magnetic field intensity produced bysaid magnet at the location of each said sensor; a processor including anon-transitory memory operating under the control of an executableprogram residing in said memory for receiving and analyzing the outputsignal from each sensor to obtain a magnetic field profile produced bythe magnet; and a transmitter for sending a data message generated bysaid processor, said data message containing information describing themagnetic field profile and whether it compares identically with asignature profile stored in said memory.